全文获取类型
收费全文 | 9359篇 |
免费 | 609篇 |
国内免费 | 50篇 |
专业分类
林业 | 588篇 |
农学 | 465篇 |
基础科学 | 78篇 |
1705篇 | |
综合类 | 651篇 |
农作物 | 480篇 |
水产渔业 | 746篇 |
畜牧兽医 | 4325篇 |
园艺 | 136篇 |
植物保护 | 844篇 |
出版年
2023年 | 84篇 |
2022年 | 155篇 |
2021年 | 278篇 |
2020年 | 279篇 |
2019年 | 351篇 |
2018年 | 319篇 |
2017年 | 358篇 |
2016年 | 352篇 |
2015年 | 250篇 |
2014年 | 337篇 |
2013年 | 532篇 |
2012年 | 529篇 |
2011年 | 592篇 |
2010年 | 301篇 |
2009年 | 334篇 |
2008年 | 479篇 |
2007年 | 461篇 |
2006年 | 410篇 |
2005年 | 383篇 |
2004年 | 364篇 |
2003年 | 322篇 |
2002年 | 362篇 |
2001年 | 251篇 |
2000年 | 254篇 |
1999年 | 210篇 |
1998年 | 64篇 |
1997年 | 63篇 |
1996年 | 56篇 |
1995年 | 53篇 |
1994年 | 40篇 |
1993年 | 41篇 |
1992年 | 88篇 |
1991年 | 56篇 |
1990年 | 64篇 |
1989年 | 74篇 |
1988年 | 66篇 |
1987年 | 54篇 |
1986年 | 49篇 |
1985年 | 62篇 |
1984年 | 39篇 |
1983年 | 44篇 |
1982年 | 32篇 |
1980年 | 24篇 |
1979年 | 37篇 |
1978年 | 24篇 |
1977年 | 23篇 |
1974年 | 23篇 |
1973年 | 25篇 |
1972年 | 24篇 |
1970年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Thirty-nine grapevine cultivars widely grown in Portugal, especially in Vinhos Verdes and Douro regions, and two well known international cultivars as standards, were genotyped at 12 microsatellite loci. The number of alleles per locus ranged from 6 to 12, and the number of allelic combinations per locus from 13 to 26. The total number of unique genotypes in the 12 analysed loci was 120, having most of the cultivars (38 out of 41) at least one unique genotype in any of the loci. The microsatellite profiles were adequate to discriminate 41 cultivars. The level of observed heterozygosity at each locus varied from 70.7% to 95.1%. VVMD28 has been revealed as one of the most informative markers. Several synonymies between Spanish and Portuguese cultivars were confirmed, and some homonymies are discussed. The genetic profiles of all 41 cultivars were searched for possible parent-offspring groups. The data obtained revealed the possible descendence of Touriga Franca from Touriga Nacional and Marufo. 相似文献
992.
Aleksandra Maji? Agnese Marino Taussig de Bodonia ?uro Huber Nils Bunnefeld 《Biological conservation》2011,144(12):3018-3027
Successful carnivore conservation depends on public attitudes and acceptance levels of carnivores, and these are likely to change as circumstances change. Attitude studies repeated in time that can demonstrate such change are rare. Our study surveyed Croatian rural inhabitants in 2002 and in 2008 and analyzed their responses to detect a change in attitudes toward brown bears (Ursus arctos) over time. Important developments occurring in Croatia at the time of our research included a more centralized and more clearly defined bear management strategy, and an increase in the bear population. We constructed models to explain respondent’s value orientations, their level of perceived threat and their acceptance capacity for bears. Findings show that while value orientations and the overall level of perceived threat did not change over time, bear acceptance capacity was reduced. This suggests that the increase in the bear population and perhaps the more centralized bear management reduced respondents’ willingness to accept a larger bear population. We conclude that continuous public involvement in bear management is essential in order to maintain a feeling of control over the bear among the local population. Furthermore we argue that hunting is an important form of public involvement in the region, serving to reinforce existence and bequest values of the bear and increase its public acceptance. 相似文献
993.
Rota A Pregel P Cannizzo FT Sereno A Appino S 《Journal of Feline Medicine and Surgery》2011,13(6):448-450
This report describes an unusual case of uterine stump pyometra in a cat whose main clinical sign at presentation was abdominal straining. At the time of ovariohysterectomy, the surgeon reported that the uterine body had a purulent content. Nearly a month after the surgery the cat showed abdominal straining. The enlarged uterine stump, filled with purulent fluid, had caused a compression of the rectum and secondary intestinal sub-occlusion. Surgical revision consisted of draining the purulent content of the remnant of the uterine body and ablating as much of it as possible; checking of the ovarian pedicles revealed the presence of a small fragment of whitish tissue on the right side, which was shown to contain, by means of histological observation and immunohistochemical staining, ovarian tissue. Four months after surgical revision the queen did not show any pathological signs and 1 year later she is still in good health. 相似文献
994.
Re M Blanco-Murcia FJ Gómez de Segura IA 《Veterinary journal (London, England : 1997)》2011,190(1):66-70
The immobilisation and anaesthesia of free-ranging cattle requires the administration of appropriate drugs in small volume via rifle or dart. The objective of this randomised controlled study was to test the capacity of a concentrated combination of tiletamine-zolazepam (TZ), ketamine (K) and detomidine (D) (TZKD) to immobilise/anaesthetise calves. Following administration of low, medium and high doses of TZKD to six healthy animals IM, the time-of-onset and duration of anaesthesia were recorded, in addition to standard cardio-respiratory parameters. Two noxious stimuli were applied to assess the analgesic effect of the combination. TZKD produced a dose-dependent anaesthetic action associated with respiratory depression and moderate hypoxaemia. Total recumbency lasted from 1h (with low dose) to 2h (with medium and high doses). The findings indicate that TZKD induces anaesthesia in calves, suitable not only for animal immobilisation, but also to carry out minor surgical procedures with or without additional local analgesia. Respiratory depression was the most severe side-effect and careful patient monitoring is recommended when using this drug combination. 相似文献
995.
Pfau T Garland de Rivaz A Brighton S Weller R 《Veterinary journal (London, England : 1997)》2011,190(2):278-283
A recent survey reported an increased risk of injury in dogs participating in agility, a competitive canine sport involving different jumping activities. The aim of this study was to quantify the kinetic parameters during jump landing for commonly used obstacle types. It was hypothesised that with increasing obstacle height, the vertical force and vertical and accelerative horizontal impulse will increase as a result of a lengthened aerial phase, a more acute landing angle and the need to convert potential into forwards kinetic energy. Simultaneous kinetic and kinematic data were recorded from 11 competition agility dogs jumping over obstacle combinations of different height and inter-obstacle distance. Speed and landing angle of the second of the two consecutive jumps were successfully controlled by obstacle height and distance between obstacles. Statistical analysis showed differences between obstacles for peak vertical force, vertical impulse and accelerative horizontal impulse (increasing values with more acute landing angles). Extremely high peak vertical force was observed in the forelimbs (4.5 times bodyweight) when landing from a hurdle jump at high speed. Further detailed studies into the consequences for internal limb structures are warranted in order to clarify how this might be related to injury. 相似文献
996.
Ediane Batista da Silva Bruna Daniella de Souza Silva Jerônimo Rafael Ruiz Leon André Kipnis Isabel K.F. de Miranda Santos Ana Paula Junqueira-Kipnis 《Veterinary journal (London, England : 1997)》2011,187(2):276-278
This study evaluated the Mycobacterium tuberculosis protein antigen MPT-51, the trimeric antigen 85 (Ag85) complex, and Bacillus Calmette-Guérin (BCG) in an indirect ELISA to diagnose bovine tuberculosis (TB) from serum samples. Serum was collected from 208 intra-dermal tuberculin test (ITT)-positive and 54 ITT-negative animals from a region where bovine TB is endemic. Using the Ag85 and BCG antigens, the indirect ELISA was able to discriminate ITT-positive from ITT-negative animals. This level of discrimination was not achieved when using the MPT-51 antigen. The highest sensitivity (Se) and specificity (Sp) of the test was found when BCG was used (Se, 82%; Sp, 91%). Further work in different epidemiological settings and with larger numbers of animals will be required to validate these findings. 相似文献
997.
Patricy de Andrade Salles Silvana C. Santos Davide Rondina Mathias Weller 《Journal of veterinary science (Suw?n-si, Korea)》2011,12(2):127-132
The present study aimed at analyzing the genetic variability of indigenous goat breeds (Capra hircus) using the MHC-associated microsatellite markers BF1, BM1818, BM1258, DYMS1, and SMHCC1. The following breeds were included: Chinese Xuhuai, Indian Changthangi and Pashmina, Kenyan Small East African (SEA) and Galla, and Albanian Vendi. To examine genetic variability, the levels of heterozigosity, degrees of inbreeding, and genetic differences among the breeds were analyzed. The mean number of alleles ranged from nine in the Galla to 14.5 in the Vendi breed. The mean observed heterozygosity and mean expected heterozygosity varied from 0.483 in the Vendi to 0.577 in the Galla breed, and from 0.767 in the SEA to 0.879 in the Vendi breed, respectively. Significant loss of heterozygosity (p < 0.01) indicated that these loci were not in Hardy-Weinberg equilibrium. The mean FIS values ranged from 0.3299 in the SEA to 0.4605 in the Vendi breed with a mean value of 0.3623 in all breeds (p < 0.001). Analysis of molecular variance indicated that 7.14% and 4.74% genetic variation existed among the different breeds and geographic groups, whereas 92.86% and 95.26% existed in the breeds and the geographic groups, respectively (p < 0.001). The microsatellite marker analysis disclosed a high degree of genetic polymorphism. Loss of heterozygosity could be due to genetic drift and endogamy. The genetic variation among populations and geographic groups does not indicate a correlation of genetic differences with geographic distance. 相似文献
998.
Letícia Z. Oliveira Vera F. M. Hossepian de Lima Marcelo A. Levenhagen Ricarda M. dos Santos Terezinha I. Assump??o José O. Jacomini André F. C. de Andrade Rubens P. de Arruda Marcelo E. Beletti 《Journal of veterinary science (Suw?n-si, Korea)》2011,12(3):267-272
The objective of this study was to characterize acrosomal ultrastructure following discontinuous Percoll gradient centrifugation of cryopreserved bovine sperm. Semen was collected from six bulls of different breeds and three ejaculates per bull were evaluated. Frozen semen samples were thawed and the acrosomal region of sperm cells was evaluated by transmission electron microscopy (TEM) before (n = 18) and after (n = 18) Percoll centrifugation. The evaluation of 20 sperm heads from each of the 36 samples analyzed ensured that a large number of cells were investigated. The data were subjected to analysis of variance at a level of significance of 5%. Percoll centrifugation reduced the percentage of sperm exhibiting normal acrosomes (from 61.77 to 30.24%), reduced the percentage of sperm presenting atypical acrosome reactions (from 28.38 to 4.84%) and increased the percentage of sperm exhibiting damage in the acrosome (from 6.14 to 64.26%). The percentage of sperm with typical acrosome reactions was not significantly different before (3.70%) and after (0.67%) centrifugation. TEM distinguished four different types of acrosomal status and enabled ultrastructural characterization of acrosomal injuries. The percentage of sperm exhibiting normal acrosomes decreased and damage in the acrosome was the most frequent acrosomal injury with the Percoll gradient centrifugation protocol utilized. 相似文献
999.
Maria Fernanda de M. Costa Adriana K. Carmona Marcio F. M. Alves Timothy M. Ryan Helen M. Davies Garry A. Anderson Ron F. Slocombe 《Journal of veterinary science (Suw?n-si, Korea)》2011,12(1):21-25
Angiotensin-I converting enzyme (ACE) is a key regulator of blood pressure, electrolytes and fluid homeostasis through conversion of angiotensin I into angiotensin II. Recently, a genetic polymorphism of the ACE gene, which accounts for 47% of the variation of ACE activity in blood, has been advocated as a biomarker of athletic aptitude. Different methods of analysis and determination of ACE activity in plasma have been used in human and equine research without a consensus of a "gold standard" method. Different methods have often been used interchangeably or cited as being comparable in the existing literature; however, the actual agreement between assays has not been investigated. Therefore, in this study, we evaluated the level of agreement between three different assays using equine plasma obtained from 29 horses. Two spectrophotometric assays using Furylacryloyl-phenylalanyl-glycyl-glycine as substrate and one fluorimetric assay utilizing o-aminobenzoic acid-FRK-(Dnp)P-OH were employed. The results revealed that the measurements from the different assays were not in agreement, indicating that the methods should not be used interchangeably for measurement of equine ACE activity. Rather, a single method of analysis should be adopted to achieve comparable results and critical appraisal of the literature is needed when attempting to compare results obtained from different assays. 相似文献
1000.
da Cruz CE de Oliveira LG Boabaid FM Zimermann FC Stein G Marks F Cerva C Lieberknecht C Canal CW Driemeier D 《Journal of zoo and wildlife medicine》2011,42(3):451-459
Pekin robins (Leiothrix lutea) were once the most widely kept softbills in captivity. As a result of the Convention on the International Trade of Endangered Species of Fauna and Flora (CITES-1997), the worldwide trade of wild-caught pekin robins has been prohibited due to the depletion of native populations of this species. In Brazil, as in other countries, pekin robins imported prior to the enactment of the CITES have disappeared from aviaries because the end of the birds' natural life span has passed, and only very few captive-bred pekin robins now exist. While captive propagation fails to address the primary causes of wild bird population decline, it might help the recovery of populations of this species. This article presents records made over a 10-yr period of a captive colony of pekin robins. Emphasis is placed on the management of the flock, the ailments affecting the birds, and the findings associated with bird losses. The main causes of bird losses included rearing management failures and age-related disorders. 相似文献