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   92556篇
  免费   5807篇
  国内免费   793篇
林业   4315篇
农学   2970篇
基础科学   729篇
  12354篇
综合类   17164篇
农作物   3585篇
水产渔业   4433篇
畜牧兽医   46256篇
园艺   1456篇
植物保护   5894篇
  2021年   989篇
  2020年   1057篇
  2019年   1176篇
  2018年   1849篇
  2017年   2051篇
  2016年   1843篇
  2015年   1728篇
  2014年   1926篇
  2013年   3584篇
  2012年   3709篇
  2011年   4212篇
  2010年   2730篇
  2009年   2538篇
  2008年   3740篇
  2007年   3593篇
  2006年   3133篇
  2005年   3047篇
  2004年   2730篇
  2003年   2732篇
  2002年   2524篇
  2001年   2696篇
  2000年   2700篇
  1999年   2104篇
  1998年   846篇
  1997年   758篇
  1995年   793篇
  1994年   693篇
  1993年   694篇
  1992年   1593篇
  1991年   1771篇
  1990年   1688篇
  1989年   1631篇
  1988年   1513篇
  1987年   1562篇
  1986年   1610篇
  1985年   1437篇
  1984年   1218篇
  1983年   1037篇
  1982年   693篇
  1979年   1087篇
  1978年   845篇
  1976年   725篇
  1975年   757篇
  1974年   1026篇
  1973年   1001篇
  1972年   970篇
  1971年   897篇
  1970年   872篇
  1969年   821篇
  1967年   713篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Dogs (n = 13), which had failed to be cured of giardiosis following chemotherapeutic measures, were treated with a Giardia vaccine (2-3 injections). Clinical signs resolved between 16 and 42 days postvaccination and cessation of fecal cyst shedding was between 21 and 70 days. Vaccination is a potential method of treating giardiosis in dogs.  相似文献   
92.
Fireblight disease, caused by Erwinia amylovora was first detected in Bulgaria on quince in the region of Plovdiv in 1989. The disease was initially localized in that area but, during 1995/1997, due to favourable climate conditions, it became epidemic. Infected trees were grubbed out and destroyed. The main hosts are quince and pear (over 40% of affected trees), then apple, medlar and Cotoneaster. Containment measures undertaken by the Bulgarian NPPO are laid down in the Plant Protection Law, in Phytosanitary Regulation no. 1 for phytosanitary control, and in Phytosanitary Regulation no. 5 of 1996 (amended 1997) for containment of fireblight. Phytosanitary control is mainly focused on fruit‐tree nurseries and on the distribution of healthy plants for planting. In 2003, 41 protected zones and 29 protected sectors within infested areas have been established.  相似文献   
93.
OBJECTIVE: To develop an efficient and reliable method that accurately differentiates bovine lymphocytes from monocytes in leukograms. SAMPLE POPULATION: Blood samples from 30 healthy cows and 1 calf with bovine leukocyte adhesion deficiency. PROCEDURE: Flow cytometric analysis of intracellular complexity and CD45 expression on bovine leukocytes was compared with results for conventional light microscopy methods. Verification of leukocyte subpopulations determined by intracellular complexity and CD45 expression was conducted, using 2-color phenotypic analysis with selected monoclonal antibodies. RESULTS: The CD45 and side-scatter properties of bovine leukocytes clearly differentiated cell types, including neutrophils, eosinophils, monocytes, and lymphocytes. CONCLUSIONS AND CLINICAL RELEVANCE: This is a rapid assay that is simple to use. More importantly, it is more accurate than the conventional method that involves the use of blood slides and light microscopy, because of the ability of the assay to readily distinguish bovine monocytes and lymphocytes. Rapid preparation of samples and short analysis times allow for efficient and reliable examination of a large number of samples, and the task of viewing slides by light microscopy is eliminated. The labor-savings benefit of this procedure is most apparent in research environments that require frequent processing of batches of blood samples.  相似文献   
94.
Genetic diversity within and among 20 herbicide-resistant (HR) and 16 herbicide-susceptible (HS) Avena fatua multi-field populations was determined using 82 polymorphic loci resulting from two intersimple sequence repeat (ISSR) primers and one long-primer random amplified polymorphic DNA (LP-RAPD) primer. Collections from the Red River Valley of North Dakota and Minnesota, sampled in 1964 and 2000, represented A. fatua populations before and after intensive exposure to herbicides. A 1995 collection from south-west North Dakota represented A. fatua exposed to low herbicide selection. Despite differences in years of herbicide exposure among collections, both HR and HS populations from every collection maintained nearly similar levels of ISSR and RAPD diversity. Genetic differentiation among populations (GST) varied from 11% to 13% among HR populations and from 9% to 16% among HS populations, indicating that 84–91% of total variation remained within HS or within HR populations. Minimal difference in gene diversity between HR and HS is consistent with multiple origins of resistance, where HR A. fatua most likely evolved from diverse founding individuals.  相似文献   
95.
96.
97.
98.
99.
Severe heart disease may cause hypotension and hypoperfusion, and ultimately circulation may cease altogether. These two clinical syndromes are cardiogenic shock and cardiac arrest, respectively. This review summarizes the causes and clinical features of each, and describes the treatment options available to clinicians managing patients in cardiogenic shock.  相似文献   
100.
In New Zealand, the brushtail possum (Trichosurus vulpecula) is the principal wildlife vector of bovine tuberculosis. Control of infected possum populations contributes to the control of tuberculosis in domestic livestock. Vaccination is potentially a complementary strategy to population control, but to be cost-effective, administration of the vaccine to possums would need to be from an appropriately designed automatic vaccinator. Possums themselves would activate the vaccinator so that it would deliver an aerosol spray of vaccine. There would be no direct way to prevent possums receiving multiple doses of vaccine. This study examined the effect on protective immunity of repeated vaccination. Captive possums were vaccinated with BCG strain pasteur 1173P2 either 12 times at weekly intervals, twice at 6-weekly intervals, or once. Vaccination was by a combination of intranasal aerosol and conjunctival instillation. Eight weeks after the last dose of vaccine, all possums were challenged intratracheally with Mycobacterium bovis strain 83/6235. Vaccination induced a significant immune response as measured by the lymphocyte proliferation assay (LPA). A significant level of protection, as measured by the response to challenge, developed in all the vaccinated possum groups, but protection was greatest in the group vaccinated 12 times. It was concluded that protection would be enhanced if vaccinations were repeated at short intervals (weekly), but no benefit or detriment resulted from revaccination after longer intervals (1-2 months).  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