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   17720篇
  免费   915篇
  国内免费   21篇
  18656篇
  2023年   119篇
  2022年   295篇
  2021年   457篇
  2020年   273篇
  2019年   280篇
  2018年   439篇
  2017年   455篇
  2016年   544篇
  2015年   746篇
  2014年   823篇
  2013年   1154篇
  2012年   1270篇
  2011年   1139篇
  2010年   687篇
  2009年   636篇
  2008年   742篇
  2007年   750篇
  2006年   646篇
  2005年   553篇
  2004年   514篇
  2003年   430篇
  2002年   393篇
  2001年   378篇
  2000年   341篇
  1999年   271篇
  1998年   147篇
  1997年   125篇
  1996年   107篇
  1995年   131篇
  1994年   110篇
  1993年   102篇
  1992年   245篇
  1991年   241篇
  1990年   219篇
  1989年   203篇
  1988年   188篇
  1987年   188篇
  1986年   168篇
  1985年   195篇
  1984年   186篇
  1983年   126篇
  1982年   123篇
  1981年   109篇
  1980年   99篇
  1979年   163篇
  1978年   118篇
  1977年   104篇
  1974年   129篇
  1973年   101篇
  1972年   105篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Core(s) and triradii of dermatoglyphic whorl patterns were joined together to form triangles. Base angles of these triangles were measured (in degrees). The tangent angle at the lower edge of a ridge crossing the core-triradius line was also measured in degrees on each side of the whorl. Significant differences and similarities of these angles were investigated for unrelated Caucasian males and females by the use of Student's t- and Pearson's r-tests. Angular findings were related to the corresponding information provided by ridge counts. Similarities and differences between males and females are described.  相似文献   
102.
103.
Summary Hagfish hemoglobin has three main components, one of which is Hb III. It is monomeric and consists of 148 amino acid residues (M = 17 350). Its complete primary structure, previously published, is discussed here. The proximal amino acid (F8) of the heme linkage is histidine as always in the hemoglobins, but the regularly expected distal histidine E7 is substituted by glutamine. This substitution, leading to a new kind of heme linkage, has hitherto only been demonstrated in opossum hemoglobin. It is suggested that E7, Gln, is directed out of the heme pocket, and that the adjacent Ell, Ile, is directed toward the inside of the pocket, giving the distal heme contact instead of histidine.Myxine Hb III has an additional tail of 9 amino acid residues at its N-terminal end, as has the hemoglobin ofLampetra fluviatilis. The genetic codes ofMyxine andLampetra hemoglobins show 117 differences, in spite of many morphological resemblances between hagfish and lamprey. Their primary hemoglobin structures show differences substantial enough to bo compatible with the divergence of the two families some 400–500 million years ago.  相似文献   
104.
Summary The chemical equilibrium and E value for Zn was calculated in 9 soils of Haryana (India) which represented mainly entisol and inceptisols. The rate of isotopic exchange between65Zn and native soil Zn was quite rapid and radioactivity reduced to about 0.2 per cent of initial activity after 3 days but total Zn concentration in soil solution did not decrease. In 5 out of 9 soils equilibrium was established in 2 to 3 days. In typic ustochrepts having high clay content (3,4) equilibrium was attained in two days. In typic udipsamments (2), typic camborthids (8) and aquic vertic ustichrepts (9) it took 3 days to set equilibrium. Typic ustochrepts (5) took 5 days for equilibrium whereas typic ustipssaments (6) and typic camborthids of high O.C. did not attain equilibrium even in 7 days. This indicated that the chemistry and availability of Zn in soil would depend on soil types. When ZnE was estimated by applying activity after equilibrium with carrier Zn and by applying activity with carrier Zn before equilibrium was set, there was no agreement in ZnE in two methods. Increasing ZnE with increasing Zn dose was observed by both methods only in alkaline typic ustochrept (4). In some soils higher E values than added amounts were observed, whereas, in soil 8 negative E values were obtained. The E values become erratic and are over estimated where complex reactions take place due to high pH, high O.C. and high complex forming elements.  相似文献   
105.
Closure of a Waterston shunt can usually be performed at the time of corrective surgery, either from the inside of the aorta or by detaching it from outside the aorta and patching the pulmonary artery. We propose a different approach for closing the shunt and repairing pulmonary artery stenosis.  相似文献   
106.
107.
Trends in the time course, changes in the moisture, soluble amino acids, proline, abscisic acid contents and nitrate reductase activity determined byin vivo method in the developing seeds of wheat were studied. Maximum dry matter augmentation in the seed took place in the period between 10–30 days after anthesis. Per cent moisture and moisture content started declining 15 days and 25 days after anthesis, respectively. Levels of soluble amino acids, proline and nitrate reductase activity were higher during initial stages of seed development, but decreased with increasing magnitude of dehydration and accumulation of abscisic acid (ABA) in the maturing seeds.  相似文献   
108.
109.
110.
Salt distribution around roots of wheat under different transpiration rates   总被引:2,自引:0,他引:2  
Summary Magnitude of Na and Cl accumulation around wheat roots was studied under different transpiration conditions in a loamy sand soil salinized with sodium chloride to an electrical conductivity of 4.1 mmho/cm in the saturation extract. A significant correlation was observed between rate of water loss per unit root length and Na and Cl content of the soil closely adhering to the roots. Under high transpiration condition, maximum ion accumulation occurred in the apparent free space of roots followed by the soil closely adhering to the roots. Results indicate that salt concentration at the root surface is markedly altered under the influence of transpiration rate such that under high transpiration conditions, the plant roots may be exposed to a much higher salt concentration than that anticipated from an analysis of the bulk soil samples.Department of Soil and Water EngineeringDepartment of Soils  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