全文获取类型
收费全文 | 127239篇 |
免费 | 7026篇 |
国内免费 | 126篇 |
专业分类
林业 | 5293篇 |
农学 | 3624篇 |
基础科学 | 720篇 |
14078篇 | |
综合类 | 23497篇 |
农作物 | 4740篇 |
水产渔业 | 5708篇 |
畜牧兽医 | 67710篇 |
园艺 | 1478篇 |
植物保护 | 7543篇 |
出版年
2018年 | 1805篇 |
2017年 | 1918篇 |
2016年 | 1675篇 |
2015年 | 1527篇 |
2014年 | 1830篇 |
2013年 | 4751篇 |
2012年 | 3420篇 |
2011年 | 4184篇 |
2010年 | 2630篇 |
2009年 | 2720篇 |
2008年 | 4061篇 |
2007年 | 3883篇 |
2006年 | 3653篇 |
2005年 | 3359篇 |
2004年 | 3255篇 |
2003年 | 3370篇 |
2002年 | 3127篇 |
2001年 | 3738篇 |
2000年 | 3796篇 |
1999年 | 3017篇 |
1998年 | 1228篇 |
1997年 | 1194篇 |
1995年 | 1336篇 |
1994年 | 1174篇 |
1993年 | 1212篇 |
1992年 | 2509篇 |
1991年 | 2839篇 |
1990年 | 2650篇 |
1989年 | 2659篇 |
1988年 | 2413篇 |
1987年 | 2436篇 |
1986年 | 2536篇 |
1985年 | 2511篇 |
1984年 | 1961篇 |
1983年 | 1778篇 |
1982年 | 1191篇 |
1979年 | 1898篇 |
1978年 | 1492篇 |
1977年 | 1362篇 |
1976年 | 1266篇 |
1975年 | 1376篇 |
1974年 | 1752篇 |
1973年 | 1736篇 |
1972年 | 1738篇 |
1971年 | 1607篇 |
1970年 | 1630篇 |
1969年 | 1502篇 |
1968年 | 1355篇 |
1967年 | 1347篇 |
1966年 | 1188篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
162.
163.
164.
165.
Shorr E 《Science (New York, N.Y.)》1940,91(2361):321-322
166.
Intrajugular injection of a purified E. coli lipopolysaccharide induced a biphasic fever in sheep after a latent period of 12 to 20 min. The changes in the blood flow from the liver and from the viscera drained by the portal vein were: (a) in the latent period, decreases in total hepatic blood flow (THF) due to decreased portal venous blood flow (PVF); (b) during the first febrile phase, increases in THF due to increased hepatic arterial blood flow and, (c) in the second febrile phase, increases in THF due to decreased PVF. Although there were large variations in the oxygen supply to the viscera drained by the portal vein and to the liver, there were relatively small or no changes in their oxygen consumption. 相似文献
167.
E M Aburto A Cribb I C Fuentealba B O Ikede F S Kibenge F Markham 《Canadian journal of veterinary research》2001,65(2):104-110
This study evaluates the ability of selenium (Se) supplementation to prevent experimental copper (Cu)-induced hepatocellular damage. Weanling male Fischer 344 rats were randomly assigned to groups of 15, 3 groups (A,B,C) were fed Cu-loaded diets (containing 2000 microg/g copper, added as CuSO4) and different levels of Se (added as Na2SeO3 x 5H2O) as follows: A) Cu-loaded/Se adequate diet (0.4 microg/g Se, fed basis); B) Cu-loaded/Se-supplemented diet (2 microg/g Se); and C) Cu-loaded/Se-deficient diet (< 0.2 microg/g). Three additional groups (D,E,F) were fed diets containing adequate levels of Cu (14 microg/g Cu, fed basis) and different levels of Se as follows: D) Cu-adequate/Se-adequate diet; E) Cu-adequate/Se-supplemented diet (2 microg/g Se); and F) Cu-adequate/Se-deficient (< 0.2 microg/g) diet. After 4, 8, and 12 weeks on the experimental diets, liver samples were processed for histology, histochemistry, metal analysis, glutathione peroxidase (GSH-Px) measurement, and quantification of malondialdehyde (MDA). Morphologic changes characteristic of Cu-associated hepatitis, without an increase in hepatic MDA levels, were seen in all Cu-loaded rats in each sampling. Similar changes occurred in rats fed Se-adequate, Se-supplemented and Se-deficient diets. This study demonstrates that Fischer 344 rats fed 2000 microg/g Cu develop morphologic changes due to Cu toxicity without evidence of lipid peroxidation. Furthermore, Se supplementation does not result in protection against Cu-induced liver injury. 相似文献
168.
169.
E C?té 《Veterinary Clinics of North America: Small Animal Practice》2001,31(6):1129-45, v
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
170.
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