全文获取类型
收费全文 | 108796篇 |
免费 | 6833篇 |
国内免费 | 1072篇 |
专业分类
林业 | 4955篇 |
农学 | 4944篇 |
基础科学 | 1303篇 |
13683篇 | |
综合类 | 19073篇 |
农作物 | 4312篇 |
水产渔业 | 5922篇 |
畜牧兽医 | 53548篇 |
园艺 | 1956篇 |
植物保护 | 7005篇 |
出版年
2021年 | 1014篇 |
2020年 | 1176篇 |
2019年 | 1479篇 |
2018年 | 2094篇 |
2017年 | 2487篇 |
2016年 | 2185篇 |
2015年 | 2050篇 |
2014年 | 2410篇 |
2013年 | 4671篇 |
2012年 | 4023篇 |
2011年 | 4769篇 |
2010年 | 3439篇 |
2009年 | 3270篇 |
2008年 | 4524篇 |
2007年 | 4219篇 |
2006年 | 3984篇 |
2005年 | 3427篇 |
2004年 | 3055篇 |
2003年 | 3085篇 |
2002年 | 2819篇 |
2001年 | 4011篇 |
2000年 | 3916篇 |
1999年 | 3042篇 |
1998年 | 1185篇 |
1997年 | 1237篇 |
1996年 | 1042篇 |
1995年 | 1200篇 |
1994年 | 1070篇 |
1993年 | 1020篇 |
1992年 | 2092篇 |
1991年 | 2216篇 |
1990年 | 2089篇 |
1989年 | 2063篇 |
1988年 | 1826篇 |
1987年 | 1855篇 |
1986年 | 1828篇 |
1985年 | 1672篇 |
1984年 | 1354篇 |
1983年 | 1140篇 |
1982年 | 790篇 |
1979年 | 1170篇 |
1978年 | 888篇 |
1975年 | 873篇 |
1974年 | 955篇 |
1973年 | 913篇 |
1972年 | 850篇 |
1971年 | 856篇 |
1970年 | 841篇 |
1969年 | 836篇 |
1967年 | 768篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
F Marco-Jiménez S Puchades E Mocé MP Viudes-de-Cartro JS Vicente M Rodriguez 《Reproduction in domestic animals》2004,39(6):438-441
Egg yolk is a common additive to sperm cryopreservation diluents. Because of its animal origin, however, it also represents a potential risk of microbiological contamination in the diluent. This potential contamination can be avoided by using powdered egg yolk, instead of fresh egg yolk, as it is pasteurized. This study was conducted to determine ram sperm cryosurvival was affected by the type of egg yolk used (powdered egg yolk or fresh egg yolk) and by yolk concentration (10, 15 or 20%) in the diluent. Microbiological analyses were also performed to quantify the microbiological contamination in the diluents containing the two types of egg yolk. Sperm cryosurvival was determined by motility and morphology analyses after thawing. Motility parameters were assessed using a computer-assisted sperm analysis (CASA) system, and the percentage of sperm with a normal apical ridge was evaluated using a differential interference contrast microscope. No significant differences were observed between diluents in the percentage of sperm with normal apical ridge. However, higher percentages of total motile cells were observed for samples containing powdered egg yolk (69%) compared to samples containing fresh egg yolk (60%). However, sperm in diluents containing fresh egg yolk, exhibited higher values for average-path velocity, straight-line velocity and beat cross frequency and lower values for amplitude of lateral head displacement (p <0.05), compared to cells in diluents containing powdered egg yolk. Microbiological contamination was similar (<200 CFU/ml) in both diluents, and no bacterial growth was observed in either, when antibiotics were added. Therefore, powdered egg yolk can be effective used in diluents for the freezing of ram semen. However, the in vivo fertility of sperm frozen in diluents containing powdered egg yolk should be tested, as some motility parameters were different for sperm treated with powdered egg yolk compared to fresh egg yolk. 相似文献
993.
Cloning and characterization of a bovine genomic fragment homologous to epidermal growth factor genes 下载免费PDF全文
S.J. John B.F. Benkel S. Bilodeau-Goeseels 《Canadian journal of veterinary research》2004,68(4):293-301
Epidermal growth factor (EGF) is a potent mitogen for a variety of cell types. The 53-amino acid mature EGF protein is encoded by sequences in exons 20 and 21 of a gene spanning over 110 kb. In this study, we report the cloning and characterization of 7.5 kb of bovine genomic sequence homologous to exon 19 through 21 from EGF genes from other mammalian species. The cloned gene fragment had an unusual sequence composition in the form of an in-frame TGA codon in the coding sequence. The sequence was expressed at low levels in kidney tissue and the corresponding cDNA contained the TGA codon. The level of similarity between the bovine exonic sequence and the human, porcine, murine, feline, and canine corresponding sequences varied from 64% to 73%; however, when only sequences encoding the mature EGF protein were compared, the level of similarity between the bovine sequence and the sequence from these species was 59% to 66%. The sequence similarity of the deduced mature protein was lower (34% to 39%) than the sequence similarity of the deduced propeptide. Although the cloned sequences could originate from a bovine EGF pseudogene, the possibility exists that they originate from the functional EGF gene. An as yet unidentified mechanism to by-pass the stop codon would allow the synthesis of a functional EGF protein. Alternatively, the cloned sequence could originate from an EGF-like gene. 相似文献
994.
D Gavier-Widén M N?remark S Benestad M Simmons L Renstr?m B Bratberg M Elvander C H?rd af Segerstad 《Journal of veterinary diagnostic investigation》2004,16(6):562-567
Within the framework of the active surveillance for transmissible spongiform encephalopathies in sheep in Sweden, 4 cases of the atypical form of scrapie, Nor98, were identified during 2003. Nor98 is a recently recognized and poorly understood variant of scrapie, first described in Norway. The cases were positive by the rapid test (enzyme-linked immunosorbent assay). Immunohistochemical staining showed diffuse thin-granular staining of the cerebellar cortex. Western immunoblotting analysis of specimens of brain stem and cerebellum showed a light band of approximately 12 kDa. Typical scrapie was ruled out based on the confirmatory testing. The affected ewes were from 4 different flocks. They were between 7 and 9 years old. Two were of the ARQ/ARQ genotype, 1 ARR/ARQ, and 1 ARR/AHQ. Two ewes had shown ataxia, and the other 2 had no clinical signs. Whole-flock slaughter was applied, and testing of the flock mates did not reveal additional cases. Nor98 differs from typical scrapie in its epidemiology, frequency of genotypes of sheep affected, clinical signs, microscopic lesions, distribution of scrapie prion protein in the brain, and characteristics of the immunostaining and immunoblotting profiles. 相似文献
995.
Stephen J Hernandez-Divers Robert S Bakal Brian H Hickson Clarence A Rawlings Heather G Wilson MaryAnn Radlinsky Sonia M Hernandez-Divers Samuel R Dover 《Journal of zoo and wildlife medicine》2004,35(4):459-470
Seventeen Gulf of Mexico sturgeons (Acipenser oxyrinchus desotoi) underwent endoscopic sex determination, gonadal biopsy, and various reproductive surgeries as part of a conservation development plan. The fish were anesthetized with tricaine methanesulfonate (MS-222) buffered with sodium bicarbonate and maintained on a recirculating water anesthesia circuit. A 6-mm Ternamian EndoTip Cannula, placed through the ventral midline, midway between pectoral and pelvic fins, permitted the introduction of a 5-mm telescope. Swim bladder aspiration and CO2 insufflation of the coelomic cavity provided excellent observation. Second and third cannulae were placed under direct visual control, lateral and cranial or caudal to the telescope cannula. Sex determination was successfully performed in all fish; however, five of 17 sturgeons (29%) required endoscopic gonadal biopsy to confirm sex. Bilateral ovariectomy or orchidectomy was successfully performed in three males and four females. Unilateral ovariectomy and bilateral ligation of the müllerian ducts using an extracorporeal suturing technique was accomplished in an additional three females. No apparent morbidity was associated with the anesthesia or endoscopic surgery in any fish. The ability to safely perform minimally invasive reproductive surgery in fish may have important management and conservation benefits. 相似文献
996.
D. Marletta S. Bordonaro A. M. Guastella G. D'Urso 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2004,121(1):52-56
In this study we surveyed two endangered Sicilian goat breeds (Girgentana and Argentata dell'Etna) for genetic polymorphism at the CSN1S2 locus. In a total of 537 goats, we detected CSN1S2A, CSN1S2B, CSN1S2C° (CSN1S2C + CSN1S2E), CSN1S2D, CSN1S2F and CSN1S2O alleles by means of various polymerase chain reaction (PCR), allele specific‐PCR (AS–PCR) and PCR‐restriction fragment length polymorphism (RFLP) reactions with the aim of improving the knowledge of the genetic resource of these two breeds. Three and five alleles, with six and twelve genotypes, were identified at CSN1S2 locus, in Girgentana and Argentata, respectively. Argentata dell'Etna showed a higher degree of genetic variation. The allelic and genotypic distribution seems to be significantly different (p < 0.001) in the two breeds. In Argentata the rare null allele (CSN1S2O) was found at low frequency (0.033); this genetic peculiarity makes its preservation worthwhile. 相似文献
997.
Genetic diversity analysis of two buffalo populations of northern India using microsatellite markers 总被引:3,自引:0,他引:3
R. Arora B. D. Lakhchaura R. B. Prasad M. S. Tantia R. K. Vijh 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2004,121(2):111-118
The genetic diversity in two buffalo populations of northern India, the Bhadawari and the Tarai was assessed using a set of 22 heterologous (bovine) microsatellite markers. The average number of alleles across all loci in both populations was found to be 4.7, indicating that this set of 22 bovine microsatellite markers could be used to study genetic variation in buffalo species also. The overall polymorphic information content (PIC) value for these markers was 0.54. The average observed and expected heterozygosities for both populations were 0.59 and 0.64, respectively. Common alleles with varying allele frequencies in both populations also represented the genetic variability existing between Bhadawari and Tarai buffaloes. However the θ estimates for population differentiation indicated low levels of differentiation between the two populations. This was further supported by the low genetic distance (0.155) between Bhadawari and Tarai, which was calculated using Nei's standard genetic distance method. The present study on Bhadawari and Tarai populations represents a much‐needed preliminary effort that could be extended to other local buffalo populations of India as well. 相似文献
998.
T. Honda T. Nomura Y. Yamaguchi F. Mukai 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2004,121(4):242-252
The gene pool of the Japanese Black cattle has been completely closed to foreign breeds during the last 100 years. Genetic diversity of the Japanese Black cattle from 1960 to 2000 was monitored with three estimates of effective number of ancestors. Founder genome equivalent (Nge) accounts for all the causes of reduction of diversity. Effective number of founders (Nef) and non‐founders (Nenf) explain reduced diversity because of unequal genetic contributions of founders and random genetic drift in non‐founders, respectively. Further examination using gene dropping simulation was conducted to obtain information on survival of founder alleles. Unique founder alleles were dropped down along the actual pedigree with Monte Carlo procedure following Mendelian segregation rules, and generated genotypes of all the current live animals (612 959 heads). Pedigree records consisted of 2 075 188 animals was used for these analysis. The estimates of three effective numbers (Nef, Nge, and Nenf) decreased from 418.6 to 50.3, 86.6 to 7.3, and 109.2 to 8.5, respectively, during the period 1960–2000. The increasing differences between two kinds of genetic diversity indices derived from Nge and Nef showed that large part of the reduced diversity from 1980 was attributed to genetic drift caused by the intensive use of particular limited number of sires. In gene dropping analysis, probabilities of extinction of founder alleles were derived from their distributions of frequency in the current animals. Several founders showed low probabilities of allele extinction, irrespective of their relatively low genetic contributions. This suggests that these founders have lineages through which their alleles are surely transmitted to the current breed. The use of these founders as a strategy for recovering the genetic diversity was discussed. 相似文献
999.
1000.
FC-17
Cutaneous papillomatosis and carcinomatosis in the highly endangered Western Barred Bandicoot 总被引:1,自引:0,他引:1
Newcastle disease virus (NDV) has antineoplastic and immunostimulatory properties, and it is currently being clinically tested in anticancer therapy. In order to analyse the immunostimulatory effects of NDV on bovine papillomatosis, we inoculated 14 cows subcutaneously with an attenuated vaccine containing the LaSota strain of NDV (LS-NDV). Four cows with papillomatosis served as controls. Serum samples were collected from each animal 1 h preinoculation and 7 and 21 days postinoculation. In inoculated cows on days 7 and 21, the mean antibody titres were log2 2.43 ± 0.92 and 5.57 ± 0.72, respectively, by haemagglutination inhibition, and the mean levels of TNFα were 5.80 ± 4.19 and 5.39 ± 2.66 ng/mL, respectively, by WEHI-164 cytotoxicity assay. Significant differences between inoculated and control animals were evident for antibody titres on day 21 and clinical scores on day 60. A correlation was evident between the TNFα activities and clinical scores on day 21. The clinical observations at day 60 showed that the papillomas in five cows had completely resolved (36%), one animal had no alterations on clinical appearance of the tumour (7%), and papillomas in eight cows had regressed (57%). In conclusion, these results demonstrated that inoculation of LS-NDV vaccine stimulates an antibody response and a limited increase in TNFα activity and may enhance clinical recovery in bovine papillomatosis.
Funding: Scientific Research Council of Akdeniz University. 相似文献
Funding: Scientific Research Council of Akdeniz University. 相似文献