全文获取类型
收费全文 | 31912篇 |
免费 | 3950篇 |
国内免费 | 6篇 |
专业分类
35868篇 |
出版年
2021年 | 317篇 |
2019年 | 273篇 |
2018年 | 309篇 |
2017年 | 287篇 |
2016年 | 522篇 |
2015年 | 816篇 |
2014年 | 909篇 |
2013年 | 1196篇 |
2012年 | 1442篇 |
2011年 | 1346篇 |
2010年 | 864篇 |
2009年 | 816篇 |
2008年 | 1217篇 |
2007年 | 1216篇 |
2006年 | 1099篇 |
2005年 | 1078篇 |
2004年 | 1074篇 |
2003年 | 1066篇 |
2002年 | 1040篇 |
2001年 | 965篇 |
2000年 | 958篇 |
1999年 | 830篇 |
1998年 | 463篇 |
1997年 | 419篇 |
1996年 | 391篇 |
1995年 | 343篇 |
1994年 | 349篇 |
1993年 | 363篇 |
1992年 | 725篇 |
1991年 | 672篇 |
1990年 | 647篇 |
1989年 | 694篇 |
1988年 | 602篇 |
1987年 | 626篇 |
1986年 | 502篇 |
1985年 | 588篇 |
1984年 | 510篇 |
1983年 | 406篇 |
1982年 | 436篇 |
1981年 | 391篇 |
1980年 | 362篇 |
1979年 | 458篇 |
1978年 | 416篇 |
1977年 | 359篇 |
1976年 | 347篇 |
1975年 | 350篇 |
1974年 | 416篇 |
1973年 | 389篇 |
1972年 | 326篇 |
1971年 | 304篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
R Smith 《BMJ (Clinical research ed.)》1981,283(6299):1108-1110
92.
The cyanobacterium Anabaena cylindrica B629 was suspended in small glass beds and incubated in a gas-tight glass vessel outdoors under a gas atmosphere comprising carbon monoxide (0.2%), acetylene (5%), oxygen (6.5%), and nitrogen. The solution phase initially contained sodium bicarbonate (10mM) at pH 7. Under these conditions the organism continuously produced hydrogen gas for over three weeks. The temperature of the culture was maintained below 30°C and minimum night temperatures were recorded. The vessel was covered by a shadecloth, which reduced the natural illumination by approximately 70%. The system is an alternative to those requiring the strict absence of oxygen and little nitrogen, and requires virtually no attention during the incubation period. 相似文献
93.
94.
95.
A systematic study of Lycopodium s.l. shows that only flavones occur in the four genera Huperzia, Lepidotis, Lycopodium s.s. and Diphasium. The arrangement of these taxa is discussed on the basis of the distribution of tricin, selgin, chrysoeriol, luteolin and apigenin. The evolutionary significance of these results and the uniqueness of Lycopodium phenolic metabolism are outlined. 相似文献
96.
A method which uses by the cross correlation of optical signals is described for the determination of the mean velocity of somatopetally moving particles within nerve fibers. The method was validated by simulation experiments and by comparing the results with those obtained by averaging collections of velocities of individual particles. The significant contribution of the method is that it allows objective and rapid serial evaluation of mean particle velocity within individual nerve fibers with good accuracy and precision. A series of results from normal myelinated nerve fibers from Xenopus laevis is presented. Considerable variation (up to 50%) in mean velocity was found between individual nerve fibers. The mean of all determinations indicates that the mean velocity of somatopetally moving particles in axons with diameters greater than 10mum is in the region of 1.14 mum/s at a temperature of 22-24 degrees C. The findings are compared with small collection of such determinations which have been reported in the literature. 相似文献
97.
98.
Prolactin binding activity was studied in suspensions of cells which had been enzymatically dissociated from R3230AC mammary tumors, 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumors and lactating rat mammary glands. Prolactin bound specifically with high affinity (apparent binding affinity = 4.0 X 10(9) M-1) to R3230AC tumor cells. Hormone binding at room temperature was proportional to cell number and increased with time of incubation up to 120-180 min. Prolactin binding to R3230AC tumor cells from diabetic animals was reduced by about 50%. Specific prolactin binding activity was also demonstrated in preparations of cells from DMBA-induced tumors and lactating mammary gland. The levels of hormone binding in both dissociated cells and subcellular particles prepared from these tissues varied as follows: DMBA-induced tumors > lactating mammary gland > R3230AC mammary adenocarcinoma. 相似文献
99.
L S Smith C W Kern R M Halpern R A Smith 《Biochemical and biophysical research communications》1976,71(2):459-465
Isolated rat brain myelin when incubated with γ32P labelled ATP yields proteins bearing acid labile, base stable phosphoryl groups. Phosphorylated myelin basic protein can be isolated and degraded with trypsin and pronase to yield principally phosphoarginine and phosphohistidine. Only a very small amount of phosphorerine survives the base treatment used in the isolation procedure. 相似文献
100.