首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   26075篇
  免费   1564篇
  国内免费   20篇
林业   1647篇
农学   917篇
基础科学   180篇
  5017篇
综合类   2889篇
农作物   1349篇
水产渔业   1921篇
畜牧兽医   11694篇
园艺   334篇
植物保护   1711篇
  2022年   194篇
  2021年   384篇
  2020年   376篇
  2019年   346篇
  2018年   751篇
  2017年   811篇
  2016年   711篇
  2015年   545篇
  2014年   703篇
  2013年   1265篇
  2012年   1194篇
  2011年   1238篇
  2010年   808篇
  2009年   721篇
  2008年   1147篇
  2007年   1074篇
  2006年   939篇
  2005年   871篇
  2004年   776篇
  2003年   743篇
  2002年   631篇
  2001年   680篇
  2000年   666篇
  1999年   541篇
  1998年   214篇
  1997年   241篇
  1996年   184篇
  1995年   210篇
  1994年   165篇
  1993年   181篇
  1992年   334篇
  1991年   352篇
  1990年   345篇
  1989年   357篇
  1988年   324篇
  1987年   285篇
  1986年   337篇
  1985年   299篇
  1984年   242篇
  1983年   236篇
  1979年   277篇
  1978年   192篇
  1977年   180篇
  1975年   178篇
  1974年   256篇
  1973年   259篇
  1972年   280篇
  1971年   252篇
  1970年   207篇
  1969年   203篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
Genotyping of bovine leucocyte antigen DRB3.2 (BoLA-DRB3.2) in a total of 523 Norwegian Red (NR) cows from two groups selected for high protein yield and low clinical mastitis, respectively, identified 27 previously reported BoLA-DRB3.2 alleles across the groups. Significant differences in BoLA-DRB3.2 allele frequencies were found between the selection groups. Alleles *13, *18, *22 and *27 had a significantly higher frequency in cows selected for low clinical mastitis, while alleles *3, *9, *11 and *26 had a higher frequency in cows selected for high protein yield. Associations between BoLA-DRB3.2 alleles and clinical mastitis were analysed based on mastitis data from 741,072 first-lactation NR cows, of which 452 were genotyped. Alleles *22 and *26 were found to be associated with increased clinical mastitis, while alleles *7, *11, *18 and *24 had a favourable effect on mastitis resistance. Contradictory results from different studies investigating associations between BoLA-DRB3.2 alleles and mastitis indicate that future studies should focus on associations of mastitis with BoLA haplotypes rather than with single BoLA genes.  相似文献   
992.
River dolphins are especially susceptible to negative human impacts. For their conservation, attempts of relocation or procreation ex situ may become important in the future to avoid their extinction. Additional knowledge and medical experiences of river dolphin management in captivity may aid such conservation efforts. The medical records and necropsy and histopathology reports on 123 captive Amazon River dolphins (Inia geoffrensis) were re-viewed. Of these 123 animals, 105 were necropsied and 70 necropsies were supported with histopathology. Eighteen animals were not necropsied. Among wild-born animals, mortality was highest in the first 2 mo immediately postcapture and transport, accounting for 32 of 123 deaths. Pneumonia and skin lesions (cutaneous and subcutaneous ulcerations and abscesses) were the most common findings, found in 44 of 105 (42%) and 38 of 105 (36%) of gross diagnoses, respectively. At least 10 of 44 cases of pneumonia diagnosed grossly included a verminous component. Cachexia, from a variety of causes, was a major gross finding in 21 animals. Fifteen animals had histologic evidence of significant renal pathology, and this was the primary cause of death in 13 cases. Hepatic pathology was found in 18 cases, and bacterial sepsis was confirmed via histology in 16 cases. Based on these findings, it may be concluded that keys to successful maintenance of this species include 1) prophylactic anthelminthic and antibiotic therapy immediately post-capture; 2) maintenance of animals in larger enclosures than in past attempts, in compatible groups, and in facilities capable of separating aggressive animals; 3) maintenance in microbiologically hygienic water quality at all times; and 4) a proactive program of preventive medicine during the immediate postcapture, quarantine, and maintenance period of captivity.  相似文献   
993.
994.
The hypothesis that increase in dietary phytin amplifies phytin binding to protein thereby reducing protein digestion, which is alleviated by phytase, was tested. A 2 × 2 factorial arrangement of dietary treatments was used to investigate the response of growing pigs to supplemental phytase (0, or 1200 units/kg) in low- or high-phytin P diets (2.2 or 3.9 g/kg). Eight crossbred barrows (28–30 kg) were canulated and assigned to crates using a double, 4 × 4 Latin Square design. Pigs were fed each of the 4 diets at 3 times metabolic BW (0.09  BW kg 0.75) for 7 d. Ileal digesta was collected for 12 h on d 6 and d 7 by attaching plastic bags to the cannula. Feed and ileal digesta were analyzed for N, energy and P. Phytase had no effect on apparent ileal digestibility (AID) of N or AAs. The AID of some AAs was higher in the high-phytin diet, which contradicts the hypothesis that higher phytin content would have a negative impact. In contrast, the AID of P was depressed by high dietary phytin (P < 0.01) and increased by phytase (P < 0.01) more so at the higher dietary phytin resulting in a phytin × phytase interaction (P < 0.01).  相似文献   
995.
Effects of lactulose (lac) as feed additive on chyme and feces quality in pigs (reared piglets: n = 10; fattening pigs: n = 20) were tested. Furthermore, fattening pigs were experimentally infected with Salmonella Derby (orally 2.6 × 108 cfu/pig, single dose infection on 1 day) to examine potential prophylactical effects. Pigs were fed a conventional diet ad libitum (in the control group without lac, in the experimental group including lac: 28.6/26.9 g lac/kg dry matter). In piglets and fattening pigs lac intake did not alter fecal dry matter (DM) content or feces pH. Contrary to findings in human beings only small amounts of lac reached the hindgut, although higher lac concentrations were measured in ileal chyme (in piglets: 10–40 g, in fattening pigs 40–70 g lac/kg DM of chyme). Lac ingestion led neither to increased concentrations of lactic acid or volatile fatty acids (vfa) nor to reduced pH data in chyme of small intestine, but in cecum and colon contents higher vfa concentrations (significant effects in piglets) were measured. Furthermore, lac ingestion resulted in reduced ammonia levels in small and large intestine contents. But no protective effects of lac ingestion were recognized when fattening pigs were infected orally with Salmonella Derby. Due to the fact that only parts of lac reach the hindgut there are doubts, whether lac can lead to comparable dietetic effects in pigs as known from human beings (laxation, forced elimination of bacteria a.s.o.). The obtained results in pigs underline the necessity of experimental studies in the target species before substances are used and recommended for dietetic purposes in feeding of pigs.  相似文献   
996.
内蒙古荒漠草原优势牧草营养价值评价   总被引:3,自引:0,他引:3  
通过测定内蒙古荒漠草原26种优势牧草的常规养分含量、纤维组成、两极离体消化率,分析了不同牧草对放牧内蒙古白绒山羊的营养价值,同时应用随意采食量、静能估测模型计算了荒漠草原优势牧草的分级指数(GI值),对牧草进行了综合评价。结果表明:(1)用营养成分和消化率指标评定,紫花苜蓿和五星蒿的营养价值最高,其次为中间锦鸡儿、圆头藜,最次为驼绒藜;(2)紫花苜蓿、五星蒿、中间锦鸡儿、圆头藜、碱蓬、全叶马兰、蒺藜草、沙打旺、阿尔泰狗娃花9种牧草GI值较高,牛枝子、甘草、猪毛蒿、松叶猪毛菜、软毛虫实、小针茅居中,灰绿藜、冷蒿、中亚狼尾草、针茅、无芒隐子草、西藏锦鸡儿、驼绒藜、黑沙蒿、刺叶柄棘豆、芨芨草、差巴嘎蒿11种牧草的GI值较低。  相似文献   
997.
Genotypic diversity in Fusarium pseudograminearum and F. graminearum from Australia and the relationship between diversity and pathogen aggressiveness for head blight and/or crown rot of wheat were examined. Amplified fragment length polymorphism (AFLP) analysis revealed a high level of genotypic diversity within each species. Sixty-three of the 149 AFLP loci were significantly different between the two species and 70 of 72 F. pseudograminearum and 56 of 59 F. graminearum isolates had distinct haplotypes. When head blight and crown rot severity data from a recently published work on isolates representing the entire range of aggressiveness were used, only the genotypic diversity of F. pseudograminearum was significantly associated with its aggressiveness for the two diseases. Cluster analyses clearly demonstrated the polyphyletic structures that exist in both pathogen populations. The spatial diversity within F. graminearum was high within a single field, while frequent gene flow ( N m ∼ 14) and a low fixation index ( G st = 0·03) were recorded among F. pseudograminearum isolates from the adjacent states of New South Wales and Queensland. The differences in population structure between the heterothallic F. pseudograminearum (teleomorph G. coronicola ) and the homothallic F. graminearum (teleomorph G. zeae ) were not as pronounced as expected given their contrasting mating systems. Neither species was panmictic or strictly clonal. This points to sexual recombination in F. pseudograminearum , suggesting that ascospores of G. coronicola may also play a role in its biology and epidemiology.  相似文献   
998.
API 50CH and API ZYM systems were used to characterize fifty-three strains of Clavibacter michiganensis subsp. sepedonicus from different geographic locations and several reference strains of the same and different species, including other potato pathogens. Clavibacter michiganensis subsp. sepedonicus strains displayed a high level of homogeneity, both in carbohydrate utilization and in enzymatic activity. Using API 50CH and API ZYM it was possible to differentiate C. michiganensis subsp. sepedonicus strains from the remaining taxa analysed in this study, which included representative strains of the other subspecies of C. michiganensis as well as other bacterial pathogens affecting potatoes. Therefore, these systems could be used as an effective method to characterize C. michiganensis subsp. sepedonicus. Such a procedure would constitute an alternative system to the conventional nutritional and physiological identification tests currently included in the official methods employed in the European Union to detect and identify this bacterium. The results obtained with the API systems agreed with the current taxonomic classification of C. michiganensis, clearly separating sepedonicus from the other subspecies belonging to this species.  相似文献   
999.
The comparison of the histologic healing and bronchopleural fistula (BPF) complications encountered with three different BS closure techniques (manual suture, stapler and manual suture plus tissue flab) after pneumonectomy in dogs was investigated for a one-month period. The dogs were separated into two groups: group I (GI) (n = 9) and group II (GII) (n = 9). Right and left pneumonectomies were performed on the animals in GI and GII, respectively. Each group was further divided into three subgroups according to BS closure technique: subgroup I (SGI) (n = 3), manual suture; subgroup II (SGII) (n = 3), stapler; and subgroup III (SGIII) (n = 3), manual suture plus tissue flab. The dogs were sacrificed after one month of observation, and the bronchial stumps were removed for histological examination. The complications observed during a one-month period following pneumonectomy in nine dogs (n = 9) were: BPF (n = 5), peri-operative cardiac arrest (n = 1), post-operative respiratory arrest (n = 1), post-operative cardiac failure (n = 1) and cardio-pulmonary failure (n = 1). Histological healing was classified as complete or incomplete healing. Histological healing and BPF complications in the subgroups were analyzed statistically. There was no significant difference in histological healing between SGI and SGIII (p = 1.00; p > 0.05), nor between SGII and SGIII (p = 1.00; p > 0.05). Similarly, no significant difference was observed between the subgroups in terms of BPF (p = 0.945; p > 0.05). The results of the statistical analysis indicated that manual suture, stapler or manual suture plus tissue flab could be alternative methods for BS closure following pneumonectomy in dogs.  相似文献   
1000.
A non-ambulatory dog with tetraparesis following a pain episode that had evolved over 2 months was submitted for medical treatment and diagnosed with intervertebral disk disease at C3-C4 and dorsal extradural compression at C1-C2 and C3-C4 using myelography and computed tomography. The dog experienced ambulation recovery after 15 days of treatment with only electroacupuncture and Chinese herbal medicine, with marked improvement occurring after only 10 treatments. Six months of follow-up demonstrated that the dog was stable and had no recurrence of symptoms. Therefore, it was concluded that the combination of electroacupuncture and Chinese herbal medicine was responsible for motor rehabilitation.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号