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   2041篇
  免费   100篇
  国内免费   12篇
林业   168篇
农学   107篇
基础科学   25篇
  523篇
综合类   162篇
农作物   93篇
水产渔业   150篇
畜牧兽医   736篇
园艺   47篇
植物保护   142篇
  2024年   6篇
  2023年   7篇
  2022年   24篇
  2021年   39篇
  2020年   60篇
  2019年   56篇
  2018年   64篇
  2017年   64篇
  2016年   73篇
  2015年   52篇
  2014年   85篇
  2013年   128篇
  2012年   123篇
  2011年   141篇
  2010年   104篇
  2009年   103篇
  2008年   145篇
  2007年   127篇
  2006年   102篇
  2005年   91篇
  2004年   91篇
  2003年   83篇
  2002年   102篇
  2001年   34篇
  2000年   19篇
  1999年   16篇
  1998年   17篇
  1997年   14篇
  1996年   15篇
  1995年   27篇
  1994年   10篇
  1993年   12篇
  1992年   8篇
  1991年   8篇
  1990年   7篇
  1989年   6篇
  1988年   7篇
  1987年   8篇
  1985年   13篇
  1984年   7篇
  1983年   6篇
  1982年   5篇
  1981年   6篇
  1980年   6篇
  1979年   3篇
  1978年   3篇
  1977年   5篇
  1976年   4篇
  1974年   3篇
  1971年   4篇
排序方式: 共有2153条查询结果,搜索用时 15 毫秒
71.
Abstract   An alopecia and dermatopathy following pelvic fractures associated with vehicular trauma is reported in three cats. The animals presented 3–4 weeks post injury with acute hair loss, glistening appearance of the skin and erosions involving the lower back. Histological examination revealed atrophy of the hair follicles and adnexal structures and follicular telogenization, dermal fibroplasia and mild lymphocytic infiltrate, fibroplasia and inflammation in the panniculus. Vascular damage secondary to the external trauma to blood vessels supplying the skin over the lumbar region and subsequent ischaemia may represent the pathomechanism of this type of alopecia. Focal permanent hair loss can be expected.  相似文献   
72.
73.
Nonhuman primates can be naturally infected with a plethora of viruses with zoonotic potential, including retroviruses. These simian viruses present risks to both captive nonhuman primate populations and persons exposed to nonhuman primates. Simian retroviruses, including simian immunodeficiency virus, simian type D retrovirus, simian T-lymphotropic virus, and gibbon ape leukemia virus, have been shown to cause clinical disease in nonhuman primates. In contrast, simian foamy virus, a retrovirus that is highly prevalent in most nonhuman primates, has not been associated with clinical disease in naturally infected primates. Although it has been shown that human retrovirus infections with human T-lymphotropic virus and human immunodeficiency virus originated through multiple independent introductions of simian retroviruses into human populations that then spread globally, little is known about the frequency of such zoonotic events. In this article, exogenous simian retroviruses are reviewed as a concern for zoo and wildlife veterinarians, primate handlers, other persons in direct contact with nonhuman primates, and other nonhuman primates in a collection. The health implications for individual animals as well as managed populations in zoos and research institutions are discussed, the cross-species transmission and zoonotic disease potential of simian retroviruses are described, and suggestions for working safely with nonhuman primates are provided.  相似文献   
74.
Effect of lameness on milk yield in dairy cows   总被引:1,自引:0,他引:1  
OBJECTIVE: To examine the relationship between lameness and milk yield in dairy cows. DESIGN: Cohort study. ANIMALS: 531 dairy cows. PROCEDURE: Cows affected with lameness were classified into 1 of 3 groups on the basis of type of diseases or lesions observed, including interdigital phlegmon (foot rot), papillomatous digital dermatitis (foot warts), or claw lesions. Cows not affected with lameness were classified as healthy. From Dairy Herd Improvement Association records, 305-day mature equivalent milk yield data were collected at the end of lactation or when the cow left the herd. Milk yield was compared between cows affected with lameness and healthy cows. RESULTS: 167 (31%) cows were affected with lameness during lactation. Lame cows had claw lesions (60%), papillomatous digital dermatitis (31%), or interdigital phlegmon (9%). Milk yield in lame cows with interdigital phlegmon (mean, 17,122 lb) was significantly less, compared with healthy cows (19,007 lb). CONCLUSIONS AND CLINICAL RELEVANCE: In this herd, interdigital phlegmon was associated with a 10% decrease in milk production. Lame cows with claw lesions or papillomatous digital dermatitis produced less milk than healthy cows, but the difference was not significant.  相似文献   
75.
OBJECTIVE: To determine the effect of two doses of fentanyl, administered transdermally, on the minimum alveolar concentration (MAC) of isoflurane in cats. STUDY DESIGN: Prospective, randomized study. ANIMALS: Five healthy, spayed, female cats. METHODS: Each cat was studied thrice with at least 2 weeks between each study. In study 1, the baseline isoflurane MAC was determined in triplicate for each cat. In studies 2 and 3, isoflurane MAC was determined 24 hours after placement of either a 25 or 50 microg hour(-1) fentanyl patch. In each MAC study, cats were instrumented to allow collection of arterial blood and measurement of arterial blood pressure. Twenty-four hours prior to studies 2 and 3, a catheter was placed and secured in the jugular vein and either a 25 or 50 microg hour(-1) fentanyl patch was placed in random order on the left thorax. Blood samples for plasma fentanyl determination were collected prior to patch placement and at regular intervals up to 144 hours. After determination of MAC in studies 2 and 3, naloxone was administered as a bolus dose (0.1 mg kg(-1)) followed by an infusion (1 mg kg(-1) hour(-1)) and MAC redetermined. RESULTS: The baseline isoflurane MAC was 1.51 +/- 0.21% (mean +/- SD). Fentanyl (25 and 50 micro g hour(-1)) administered transdermally significantly reduced MAC to 1.25 +/- 0.26 and 1.22 +/- 0.16%, respectively. These MAC reductions were not significantly different from each other. Isoflurane MAC determined during administration of fentanyl 25 micro g hour(-1) and naloxone (1.44 +/- 0.16%) and fentanyl 50 micro g hour(-1) and naloxone (1.51 +/- 0.19%) was not significantly different from baseline MAC (1.51 +/- 0.21%). CONCLUSIONS AND CLINICAL RELEVANCE: Fentanyl patches are placed to provide long-lasting analgesia. In order to be effective postoperatively, fentanyl patches must be placed prior to surgery. Plasma fentanyl concentrations achieved intraoperatively decrease the need for potent inhalant anesthetics in cats.  相似文献   
76.

Background

Soundness of an individual horse is important for animal welfare and owner economy. However, knowledge of health status in normal horse populations is limited due to lack of systematic health recordings. The aim of the investigation was to study the prevalence of veterinary clinical findings in 4-5-year-old Swedish warmblood riding horses, and their influence on overall health scores, where associations to future longevity has been indicated.

Results

The prevalence of clinical findings in 8,281 horses examined during 1983–2005 was studied according to a standardised protocol and related to overall health scores in linear statistical models. Effects of sex, age, examination event and changes over time were included. In total, 49% of the horses had clinical findings of medical health (MED), 42% in hooves (HOOF) and 74% of palpatory orthopaedic health (PALP). However, only 6%, 3% and 24% had moderate or severe findings, of MED, HOOF and PALP, respectively. Flexion test reactions were reported in 21% of the horses (5% moderate/severe), heavily influencing the overall score (H2). One fifth of these horses also had findings of unprovoked lameness while 83% had PALP findings (44% with moderate/severe findings). Acute clinical signs, i.e. heat or soreness, had a large influence on the H2 score but were rare, whereas more common clinical findings had smaller effects on overall health. Large variations in recorded health results were observed among events. A decrease in findings has occurred since 1983, in particular for PALP findings.

Conclusions

Results of occurrence and relevance of evaluated clinical findings could be used for advice on preventive actions to keep horses sound, and possibly for benchmarking, and genetic evaluation of health traits. The distinct effect of event on recorded clinical findings emphasises that further harmonisation of veterinary examinations are desirable.  相似文献   
77.
Abstract

Four processed soybean products were evaluated as protein sources for Atlantic salmon: solvent-extracted soybean meal (SBM44), dehulled and solvent-extracted soybean meal (SBM50), dehulled full-fat soybean meal (FFSBM) and soybean concentrate (SBC). The soybean products replaced high-quality fish meal at levels corresponding to 0, 14, 28, 42 and 56% soybean protein of total protein.

Dietary inclusion of SBC, at the expense of fish meal, did not affect weight gain, carcass lipids, fecal excretion of nutrients or fecal dry matter content significantly. The nutritive value of the SBC protein appeared comparable to that of the fish meal. The three other soybean products impaired performance increasingly with increasing levels of inclusion, indicating lower nutritive value than for the fish meal. The favourable results seen with SBC indicated a great potential of soybean to become an important protein source for Atlantic salmon through improved processing.  相似文献   
78.
The serine proteases, tissue‐ and urokinase‐type plasminogen activators (PLAT and PLAU) and their inhibitors SERPINE1/2 are regulators of plasminogen to plasmin conversion. They are widely expressed in ovarian tissues, including granulosa and cumulus cells, and their expression is regulated by gonadotropins. The aim of this work was to assess the effect of serine protease inhibitors (aprotinin and AEBSF) and SERPINE1/2 on FSH‐induced cumulus cell expansion, the production of prostaglandin E2 (PGE2) and retention of hyaluronic acid (HA) in expanding cumulus. The serine protease activity proved to be essential for the production of PGE2 and also for the retention of HA; the inhibition of plasminogen activators by SERPINE1/2 had the same effect. Collectively, these data indicate that plasmin is required for proper function of expanding cumulus cells in vitro and presumably also in vivo in the pre‐ovulatory follicles.  相似文献   
79.
Human epidermal growth factor 2 (HER2) overexpression leads to aggressive mammary tumour growth. Although the prognosis of HER2+ tumours in humans is greatly improved using biologicals, therapy resistance, which may be caused by increased phosphatidyl‐3‐kinase (PI3K), rous sarcoma proto‐oncogene (cSRC) or wingless‐type MMTV integration site family (Wnt) activity, is a major concern. A recent analysis of 12 canine mammary cell lines showed an association between HER2/3 overexpression and phosphatase and tensin homologue (PTEN) deletion with elevated Wnt‐signalling. Wnt‐activity appeared to be insensitive to phosphatidyl‐3‐kinase (PI3K) inhibitors but sensitive to Src‐I1. We hypothesized that Wnt activation, was caused by HER2/3‐activated cSRC activation. The role of HER2/3 on Wnt signalling was investigated by silencing HER2/3 expression using specific small interfering RNA (siRNAs). Next, the effect of an epidermal growth factor receptor (EGFR)/HER2 tyrosine kinase inhibitor on Wnt activity and migration was investigated and compared to other tyrosine kinase inhibitors (TKIs) of related signalling pathways. Finally, two TKIs, a cSRC and a PI3K inhibitor, were investigated in a zebrafish xenograft model. Silencing of HER1‐3 did not inhibit the intrinsic high Wnt activity, whereas the HER kinase inhibitor afatinib showed enhanced Wnt activity. The strongest inhibition of Wnt activity and cell viability and migration was shown by cSRC inhibitors, which also showed strong inhibition of cell viability and metastasis in a zebrafish xenograft model. HER2/3 overexpression or HER2/3‐induced cSRC activation is not the cause of enhanced Wnt activity. However, inhibition of cSRC resulted in a strong inhibition of Wnt activity and cell migration and metastasis. Further studies are needed to unravel the mechanism of cSRC activation and cSRC inhibition to restore sensitivity to HER‐inhibitors in HER2/3‐positive breast cancer.  相似文献   
80.
Background: Long non-coding RNAs(lncRNAs) may regulate gene expression in numerous biological processes including cellular response to xenobiotics.The exposure of living organisms to 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD),a persistent environmental contaminant,results in reproductive defects in many species including pigs.The aims of the study were to identify and characterize lncRNAs in porcine granulosa cells as well as to examine the effects of TCDD on the lncRNA expression profile in the cells.Results: One thousand six hundred sixty-six lncRNAs were identified and characterized in porcine granulosa cells.The identified lncRNAs were found to be shorter than mRNAs.In addition,the number of exons was lower in lncRNAs than in m RNAs and their exons were longer.TCDD affected the expression of 22 lncRNAs(differentially expressed lncRNAs [DELs]; log2 fold change ≥ 1,P-adjusted 0.05) in the examined cells.Potential functions of DELs were indirectly predicted via searching their target cis-and trans-regulated protein-coding genes.The coexpression analysis revealed that DELs may influence the expression of numerous genes,including those involved in cellular response to xenobiotics,dioxin metabolism,endoplasmic reticulum stress and cell proliferation.Aryl hydrocarbon receptor(AhR) and cytochrome P450 1 A1(CYP1 A1) were found among the trans-regulated genes.Conclusions: These findings indicate that the identified lncRNAs may constitute a part of the regulatory mechanism of TCDD action in granulosa cells.To our knowledge,this is the first study describing lncRNAs in porcine granulosa cells as well as TCDD effects on the lncRNA expression profile.These results may trigger new research directions leading to better understanding of molecular processes induced by xenobiotics in the ovary.  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