全文获取类型
收费全文 | 275993篇 |
免费 | 30237篇 |
国内免费 | 258篇 |
专业分类
306488篇 |
出版年
2016年 | 3079篇 |
2015年 | 4295篇 |
2014年 | 4849篇 |
2013年 | 7377篇 |
2012年 | 7935篇 |
2011年 | 8190篇 |
2010年 | 5427篇 |
2009年 | 5003篇 |
2008年 | 7416篇 |
2007年 | 7523篇 |
2006年 | 7158篇 |
2005年 | 6909篇 |
2004年 | 6815篇 |
2003年 | 6598篇 |
2002年 | 6389篇 |
2001年 | 11749篇 |
2000年 | 11791篇 |
1999年 | 9326篇 |
1998年 | 3387篇 |
1997年 | 3621篇 |
1996年 | 3518篇 |
1995年 | 3126篇 |
1994年 | 3109篇 |
1993年 | 3103篇 |
1992年 | 7867篇 |
1991年 | 7852篇 |
1990年 | 7515篇 |
1989年 | 7474篇 |
1988年 | 6852篇 |
1987年 | 6601篇 |
1986年 | 6020篇 |
1985年 | 6207篇 |
1984年 | 5146篇 |
1983年 | 4338篇 |
1982年 | 3373篇 |
1981年 | 3144篇 |
1980年 | 2944篇 |
1979年 | 4950篇 |
1978年 | 3811篇 |
1977年 | 3724篇 |
1976年 | 3432篇 |
1975年 | 3785篇 |
1974年 | 4175篇 |
1973年 | 4092篇 |
1972年 | 3666篇 |
1971年 | 3435篇 |
1970年 | 3086篇 |
1969年 | 2995篇 |
1968年 | 2745篇 |
1967年 | 2370篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
232.
F García J Sánchez J Planas 《Comparative biochemistry and physiology. A, Comparative physiology》1987,87(4):947-950
1. Male quails submitted 20 and 120 days to a low iron diet (7 ppm) were compared to female laying quails, exposed for 30 days to the same low iron regime, in order to compare the response of the iron metabolic control under a single (erythropoiesis) or a doubled (erythropoiesis and egg formation) iron demand. 2. Iron deposit in storage organs, the classical hematology and the intestinal iron absorption were analyzed in these animals. 3. In males, after 120 days, the iron deposits were reduced 50 and 75%, but hematological values (hematocrit and hemoglobin concentration) were normal, although in laying quails, after 30 days, an anemic condition was evident in both blood parameters and iron deposits, provoking an iron deficient erythropoiesis. 4. The enhancement of the intestinal iron uptake, confirms the anemic character of these birds. 相似文献
233.
M Tachibana H Morioka M Machino F Mizukoshi O Mizukoshi T Yoshioka 《Histochemistry》1985,82(2):197-199
Triphosphoinositide (TPI), an aminoglycoside receptor and a possible regulator of cationic permeation through its ability to bind with Ca++, was localized by the protein-A gold technique in vestibular sensory epithelia using an antibody highly specific to TPI. TPI was detected on the stereocilia, kinocilia, and cuticular plate of hair cells, and in the reticular membrane of supporting cells. The cilia of hair cells are damaged by aminoglycosides at a relatively early stage of toxicity. Ca++-regulated bioactivity in this area is probably involved. 相似文献
234.
A Levva G Schwartsmann L C Boeije H M Pinedo F de Waal 《Biochemical and biophysical research communications》1986,141(2):629-635
In the original HL-60 cells (HL-60-S) and an HL-60 subline (HL-60-R) respectively susceptible and resistant to induction of differentiation by retinoic acid or dimethyl sulfoxide, 5-aza-2'-deoxycytidine inhibited growth equally but induced differentiation to a greater extent in HL-60-S. Flow cytometry showed that 5-aza-2'-deoxycytidine produced in both HL-60 lines an increased proportion of cells in G2+M rather than G0/G1 as with retinoic acid. 5-aza-2'-deoxycytidine may have a differentiation-inducing effect in HL-60 provided cells have the competence to differentiate, indicating the importance of an alternate mechanism of action. 相似文献
235.
I A Shabarov S N Rumiantsev V F Pospelov 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1985,(6):3-6
As the result of the study of tetanolysin-producing Clostridium tetani strains, their populations have been found to be markedly heterogeneous with respect to the hemolytic activity of clone cultures. On the basis of normal and dialyzed cultures of selected variants with maximum activity the preparations of tetanolysin have been obtained, and their hemolytic activity and antigenic properties have been studied. Antihemolytic rabbit sera have also been obtained and characterized. Partially purified preparations of tetanolysin with high hemolytic activity have been obtained by the fractionation of C. tetani dialyzed cultures with ammonium sulfate. 相似文献
236.
F. Kees M. Bucher G. Mair H. Grobecker 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2001,753(2):50
A high-performance liquid chromatographic method is described for the determination of opipramol in human plasma. Opipramol was extracted into tert.-butylmethyl ether, separated on a cyanopropyl silica column and detected at 254 nm. Imipramine was used as internal standard. The limit of quantitation was 250 pg/ml using 1.5 ml plasma. Precision was better than 9%, inaccuracy less than 8%. The assay is more sensitive than previously published methods, and it has been applied to the analysis of plasma samples from a pharmacokinetic study. 相似文献
237.
How reliable are dung counts for estimating elephant numbers? 总被引:4,自引:0,他引:4
R. F. W. Barnes 《African Journal of Ecology》2001,39(1):1-9
Dung counts are the most commonly used techniques for estimating elephant numbers in forests, yet there is considerable scepticism concerning their accuracy. Published accounts of dung counts show that they give estimates similar to those from other methods for vertebrates ranging in size from lizards to elephants. For ungulates, macropods and elephants there are strong correlations between estimates from dung counts and other methods. Thus, dung counts are as accurate or inaccurate as other methods for estimating vertebrate numbers, including elephants. Dung counts for elephants give estimates that are as precise as, and sometimes more precise than, those from aerial surveys of elephants. This is because the variance in dung density is usually low and results in a lower than expected variance for the final elephant estimate when combined with the variances of defecation and decay rates. Dung counts may be more appropriate than aerial surveys for monitoring small or declining elephant populations. 相似文献
238.
239.
The p53 pathway and apoptosis. 总被引:17,自引:0,他引:17