全文获取类型
收费全文 | 2501篇 |
免费 | 218篇 |
国内免费 | 6篇 |
出版年
2021年 | 39篇 |
2020年 | 19篇 |
2019年 | 24篇 |
2018年 | 39篇 |
2017年 | 28篇 |
2016年 | 58篇 |
2015年 | 117篇 |
2014年 | 126篇 |
2013年 | 146篇 |
2012年 | 216篇 |
2011年 | 157篇 |
2010年 | 103篇 |
2009年 | 84篇 |
2008年 | 121篇 |
2007年 | 119篇 |
2006年 | 130篇 |
2005年 | 97篇 |
2004年 | 100篇 |
2003年 | 90篇 |
2002年 | 67篇 |
2001年 | 78篇 |
2000年 | 62篇 |
1999年 | 81篇 |
1998年 | 38篇 |
1997年 | 30篇 |
1996年 | 13篇 |
1995年 | 17篇 |
1994年 | 21篇 |
1993年 | 16篇 |
1992年 | 35篇 |
1991年 | 38篇 |
1990年 | 33篇 |
1989年 | 21篇 |
1988年 | 23篇 |
1987年 | 22篇 |
1986年 | 29篇 |
1985年 | 28篇 |
1984年 | 13篇 |
1983年 | 20篇 |
1982年 | 22篇 |
1981年 | 18篇 |
1980年 | 16篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1977年 | 12篇 |
1976年 | 20篇 |
1975年 | 17篇 |
1974年 | 12篇 |
1973年 | 15篇 |
1972年 | 14篇 |
排序方式: 共有2725条查询结果,搜索用时 172 毫秒
41.
Shau-Ting Chiu Lori H. Anton Frank W. Ewers Raymond Hammerschmidt Kurt S. Pregitzer 《American journal of botany》1992,79(2):149-154
Fertilized stands of Pseudotsuga menziesii were found to have glaucous needles. We investigated the morphological and quantitative characteristics of the epicuticular waxes of needles of fertilized and control trees. Glaucousness was caused by ornate tubular epicuticular wax. Dipping needles in chloroform, which dissolves waxes, eliminated the glaucous appearance. Based on cryostage scanning electron microscopic observations, the epicuticular waxes in the nonstomatal region were much more ornate on the needles of the fertilized trees (experimental needles) than in unfertilized trees (control needles). The stomatal region in both experimental and control needles showed similarly ornate waxes. Quantities of waxes were similar in experimental and control needles. The glaucousness was not the result of greater quantities of wax; rather, fertilization altered wax morphology in the nonstomatal regions. 相似文献
42.
滇黄芩甙A和B的结构 总被引:3,自引:1,他引:2
从龙胆科滇黄芩属植物滇黄芩(Veratrilla baillonii Franch)中分离得到两个新的酮二糖甙,经~1H NMR,~(13)C NMR,FAB-MS,MS,2D NMR,UV,IR等物理方法和化学反应,推定为:2,3,4,7-四甲氧基酮-1-O-β-D-葡萄糖(6←1)-β-D-木糖甙(1)和7-羟基-2,3,4-三甲氧基酮-1-O-β-D-葡萄糖(6←1)-β-D-木糖甙(2),分别命名为:滇黄芩甙A和滇黄芩甙B。 相似文献
43.
44.
P L Chiu M Mushtaq H B Weems S K Yang 《Biochemical and biophysical research communications》1984,124(1):114-120
Optically active 7-hydroxy-7,8-dihydrobenzo[a]pyrene and 8-hydroxy-7,8-dihydrobenzo[a]pyrene were identified as two of the major metabolites formed by incubation of 7,8-dihydrobenzo[a]pyrene with rat liver microsomes. Optically active 9-hydroxy-9,10-dihydrobenzo[a]pyrene and 10-hydroxy-9,10-dihydrobenzo[a]pyrene were similarly identified as two of the minor metabolites of 9,10-dihydrobenzo[a]pyrene. The formation of these metabolites was abolished either by prior treatment of liver microsomes with carbon monoxide or the absence of NADPH, but was not inhibited by an epoxide hydrolase inhibitor. The results indicate that the aliphatic carbons of dihydro polycyclic aromatic hydrocarbons may undergo stereoselective hydroxylation reactions catalyzed by the cytochrome P-450 system of rat liver microsomes. 相似文献
45.
Active and passive cation transport and L antigen hertogeneity in low potassium sheep red cells
下载免费PDF全文
![点击此处可从《The Journal of general physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Several lines of experimental evidence are presented suggesting that the L antigens in low potassium (LK) sheep red cells are associated with separate Na(+)K(+) pump flux is distinct from the action of anti-L(l) on K(+) leak flux, implying that K(+) leak transport sites may not be converted into active pumps by the L antiserum. Treatment of LK red cells with trypsin completely abolished both the stimulation of K(+) pump flux and the enhancement of the rate of ouabain binding brought about by anti- L. That this effect is due to a total destruction of the L(p) determinant associated with the LK pump was evident from the complete failure of anti-L(p) to bind to trypsinized LK red cells. The L(p) antigen can be effectively protected against the trypsin attack by prior incubation with anti-L, indicating that the sites for antibody binding and trypsin action may be closely adjacent at the structural level. Trypsin treatment, however, did not interfere with anti-L(l) reducing ouabain insensitive K(+) leak influx, nor did it prevent binding of anti-L(ly), the hemolytically active L antibody which is probably identical with anti-L(l). The functional independence of the L(p) and L(l) sites was documented by the observation that anti-L(l) still reduced K(+) leak influx in LK cells with experimentally induced high potassium concentrations, at which K(+) pump flux is fully suppressed, whether or not anti-L(p) was binding to the L(p) antigen associated with the LK pump. 相似文献
46.
A method is described for the estimation of adenosine 3′,5′-monophosphate (3′,5′-cyclic AMP) in rat brain by high-pressure liquid chromatography (HPLC). The nucleotide is purified initially by being passed through two columns, alumina and AG-1X2. The peak in HPLC was identified by a number of methods. Optimum parameters for HPLC were obtained by using 1 mm KH2PO4 buffer, pH 4.8, at a flow rate of 57 ml/hr at room temperature. Using this technique the concentration of 3′,5′-cyclic AMP in rat brain was found to be 2.53 ± 0.40 nmol/g (mean ± SD, n = 5). 相似文献
47.
Dorothy E. Pumo Ryszard Wierzbicki Adrienne Sainten Jen-Fu Chiu 《Molecular and cellular biochemistry》1980,32(1):49-53
Summary Specific antisera were produced against chicken reticulocyte dehistonized chromatin. The antisera reacts strongly with chicken reticulocyte chromatin, but only marginally with chicken erythrocyte chromatin. There is no reticulocyte antigen detected in chicken liver. Reticulocyte maturation is accompanied by a gradual decrease in the chromatin immunological activity and template capacity. The reduction of immunological activity is due to the change of chromatin conformation during erythrocyte maturation. Dehistonization and sonication of erythrocyte chromatin raises the erythrocyte chromatin immunological activity to levels similar to those of reticulocyte chromatin. The erythrocyte nuclear antigens are class specific, not being found in frog erythroid cell or murine Friend leukemia cell chromatins. 相似文献
48.
49.
Summary The sexual development of 14 girls with non-mosaic monocentric 46,X,iXq karyotype was studied. Seven out of eight girls were found to have immature secondary sexual characteristics and amenorrhoea, a finding greatly contrasting with that in Triplo-X girls. The relative ineffectiveness of the isochromosome Xq in maintaining fertility may be due to the absence of one short arm, which probably also carries a gonadal determinant. Alternatively, the presence of two inactivation sites on one isochromosome may render the gonadal determinants inactive at an important stage in gonadal development. 相似文献
50.