全文获取类型
收费全文 | 1363902篇 |
免费 | 122619篇 |
国内免费 | 1412篇 |
专业分类
1487933篇 |
出版年
2021年 | 17840篇 |
2019年 | 16166篇 |
2018年 | 17819篇 |
2017年 | 16630篇 |
2016年 | 28165篇 |
2015年 | 42488篇 |
2014年 | 50431篇 |
2013年 | 76754篇 |
2012年 | 36880篇 |
2011年 | 25224篇 |
2010年 | 43552篇 |
2009年 | 44981篇 |
2008年 | 24213篇 |
2007年 | 22016篇 |
2006年 | 27344篇 |
2005年 | 28373篇 |
2004年 | 27589篇 |
2003年 | 25138篇 |
2002年 | 23324篇 |
2001年 | 35055篇 |
2000年 | 32534篇 |
1999年 | 32526篇 |
1998年 | 25705篇 |
1997年 | 25496篇 |
1996年 | 24995篇 |
1995年 | 23138篇 |
1994年 | 22981篇 |
1993年 | 22116篇 |
1992年 | 28354篇 |
1991年 | 26540篇 |
1990年 | 25438篇 |
1989年 | 26310篇 |
1988年 | 24022篇 |
1987年 | 22845篇 |
1986年 | 21680篇 |
1985年 | 23512篇 |
1984年 | 23141篇 |
1983年 | 20459篇 |
1982年 | 20791篇 |
1981年 | 19922篇 |
1980年 | 18763篇 |
1979年 | 19310篇 |
1978年 | 18128篇 |
1977年 | 17251篇 |
1976年 | 16500篇 |
1975年 | 16017篇 |
1974年 | 16313篇 |
1973年 | 16663篇 |
1972年 | 14072篇 |
1971年 | 12781篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
162.
163.
Nitrogen fertigation of greenhouse-grown cucumber 总被引:2,自引:0,他引:2
I. Papadopoulos 《Plant and Soil》1986,93(1):87-93
Summary This greenhouse study investigated the response of trickle-irrigated cucumber (Cucumis sativa cv. ‘Petita’) to three N levels applied with every irrigation via the irrigation stream. The plants were grown in pots filled
with 12 kg of soil. Water containing 5.8, 11.8, or 17.8 mmol N/l, and uniformly supplied with 2.0 and 3.9 mmol/l of P and
K, respectively, was applied two to three times daily. In all treatments of 0.3 leaching fraction was allowed.
The resulting total N applications were 15.7, 31., and 47.2 g N/plant. The total amount of water applied was 1851/plant. Total
N and NO3-N, in lajinae and petioles, increased with increasing N level whereas P and K in generated decreased. Although different
NO3/NH4 ratios in the treatments may have influeced the response to N, it could be concluded that the highest yield was obtained
with 11.8 mmol N/1 due to increased number of fruit. In the root volume of this treatment the NO3-N concentration in the soil solution was aroun 7 mmol/1 for most of the growing season. The dry matter concentration of fruits
was not affected by the N levels.
It was concluded that 11.8 mmol N/1 applied with every irrigation via the irrigation stream is adequate to cover the needs
of greenhous-grown cucumber for higher yield (9.42 kg/plant over a harvesting period of 93 days). 相似文献
164.
OBJECTIVE--To test the hypothesis that farmers are at high risk of hip osteoarthritis and to investigate possible causes for such a hazard. DESIGN--Cross sectional survey. SETTING--Five rural general practices. SUBJECTS--167 male farmers aged 60-76 and 83 controls from mainly sedentary jobs. All those without previous hip replacement underwent radiography of the hip. MAIN OUTCOME MEASURES--Hip replacement for osteoarthritis or radiological evidence of hip osteoarthritis. RESULTS--Prevalence of hip osteoarthritis was higher in farmers than controls and especially in those who had farmed for over 10 years (odds ratio 9.3, 95% confidence interval 1.9 to 44.5). The excess could not be attributed to any one type of farming, and heavy lifting seems the likely explanation. CONCLUSIONS--Manual handling in agriculture should be limited where possible. Consideration should be given to making hip osteoarthritis a prescribed industrial disease in farmers. There may be wider implications for the prevention of hip osteoarthritis in the general population. 相似文献
165.
Synthesis of prenylquinones in chloroplasts 总被引:3,自引:0,他引:3
166.
CONSENSUS CLADOGRAMS AND GENERAL CLASSIFICATIONS 总被引:2,自引:0,他引:2
167.
168.
169.
An earlier report (1) of an adverse effect of high doses of oxytocin on human memory included results of studies on women receiving oxytocin as part of the treatment to induce 2nd trimester therapeutic abortion. These women served as their own controls. We have now been able to study a group of women who have been treated in all ways like the original group, with the exception that they did not receive oxytocin. The results from this external control corroborate the finding that oxytocin affected memory. 相似文献
170.
Isolation of zymogen granules from rat pancreas and characterization of their membrane proteins 总被引:3,自引:0,他引:3
A zymogen granule fraction has been isolated from rat pancreas, and its purity has been assessed by biochemical and morphological criteria. Specific activities of two marker enzymes, amylase and chymotrypsin, are increased by 4.6 and 5.4-fold, respectively, as compared to the homogenate. The purified fraction is devoid of detectable RNA, DNA and 5'-nucleotidase, glucose-6-phosphatase, and cytochrome c oxidase activities. Electron micrographs confirm the absence of mitochondria, lysosomes, and rough endoplasmic reticulum fragments. Zymogen granule membranes were isolated from this fraction on a sucrose gradient following lysis in alkaline buffer. Secretory contaminants were efficiently removed from the membranes as indicated by experiments in which labeled secretory proteins were added during the isolation procedure and secondly by measuring residual levels of amylase and chymotrypsin. Three enzyme activities were found in the membranes: thiamine pyrophosphatase, ATP-diphosphohydrolase, and low levels of acid phosphatase. Membrane proteins were solubilized by urea-Triton X-100 and separated in double-dimension (isoelectric focusing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Isoelectric point and molecular weight of each protein band were determined. 相似文献