全文获取类型
收费全文 | 3499篇 |
免费 | 314篇 |
出版年
2021年 | 54篇 |
2020年 | 47篇 |
2019年 | 43篇 |
2018年 | 52篇 |
2017年 | 42篇 |
2016年 | 87篇 |
2015年 | 172篇 |
2014年 | 194篇 |
2013年 | 219篇 |
2012年 | 284篇 |
2011年 | 220篇 |
2010年 | 168篇 |
2009年 | 139篇 |
2008年 | 175篇 |
2007年 | 181篇 |
2006年 | 172篇 |
2005年 | 135篇 |
2004年 | 153篇 |
2003年 | 139篇 |
2002年 | 135篇 |
2001年 | 40篇 |
2000年 | 41篇 |
1999年 | 50篇 |
1998年 | 48篇 |
1997年 | 25篇 |
1996年 | 30篇 |
1995年 | 24篇 |
1994年 | 28篇 |
1993年 | 26篇 |
1992年 | 37篇 |
1991年 | 30篇 |
1990年 | 34篇 |
1989年 | 32篇 |
1988年 | 25篇 |
1987年 | 18篇 |
1986年 | 17篇 |
1985年 | 25篇 |
1984年 | 31篇 |
1983年 | 23篇 |
1982年 | 21篇 |
1981年 | 26篇 |
1980年 | 19篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1977年 | 14篇 |
1976年 | 24篇 |
1974年 | 22篇 |
1972年 | 13篇 |
1971年 | 14篇 |
1969年 | 13篇 |
排序方式: 共有3813条查询结果,搜索用时 15 毫秒
1.
Stefano Carenini Dirk Montag Harold Cremer Melitta Schachner Rudolf Martini 《Cell and tissue research》1996,287(1):3-9
We have previously shown that mice deficient in the gene for the myelin-associated glycoprotein (MAG) develop normal myelin
in the peripheral nerves, but show axon and myelin degeneration at eight months of age, suggesting that MAG is involved in
the maintenance of axon-Schwann cell integrity. The search for molecules that might replace MAG during myelination revealed
an overexpression of the neural cell adhesion molecule (N-CAM) at those aspects where MAG is detectable in wild type mice.
To test whether N-CAM might compensate for MAG during myelination in MAG-deficient mice, double mutants deficient in both
MAG and N-CAM (MAG−/N-CAM−mice) were generated by cross-breeding the single mutants. Whereas alterations of myelin development were not detectable in
either of the single or double mutants, degeneration of myelin and axons occurred approximately 4 weeks earlier in MAG−/N-CAM−than in MAG−mutants. Furthermore, at 8 weeks of age, single fiber preparation and electron microscopy revealed that the number of profiles
indicative of degeneration was substantially increased in MAG−/N-CAM−mutants when compared to MAG−mice. These data suggest that in MAG-deficient mice N-CAM does not compensate for MAG in myelin formation but partially substitutes
for it in the maintenance of axon-myelin integrity.
Received: 20 May 1996 / Accepted: 19 July 1996 相似文献
2.
Environmental control of flowering time in Antirrhinum majus 总被引:1,自引:0,他引:1
The effect of different environmental conditions on flowering time and the number of leaves produced before the first flower is formed has been investigated in Antirrhinum majus L. The effect of light quality has been tested by decreasing the red/far‐red ratio, generally resulting in a reduced flowering time and leaf number. Furthermore, it could be shown that photoperiod, temperature and light intensity are inversely correlated with flowering time and leaf number. However, lowering the temperature from 15 to 12°C resulted in a reduction of flowering time. This observation shows that Antirrhinum can be vernalised.
Using defined combinations of the four environmental factors we have been able to reduce flowering time to only 42 days or to delay flowering for at least 2 years. The results obtained allow an optimisation of the screening conditions for identifying flowering time mutants in Antirrhinum . 相似文献
Using defined combinations of the four environmental factors we have been able to reduce flowering time to only 42 days or to delay flowering for at least 2 years. The results obtained allow an optimisation of the screening conditions for identifying flowering time mutants in Antirrhinum . 相似文献
3.
4.
P. Marion Handford 《Journal of applied microbiology》1974,37(4):559-570
S ummary . This paper describes the development and use of a selective diagnostic medium for the detection and enumeration of Clostridium perfringens in foods. The medium gives higher counts of Cl. perfringens and fewer false positives than existing media. 相似文献
5.
6.
Hot-water treatment before tissue culture reduces initial contamination in Lilium and Acer 总被引:10,自引:0,他引:10
Langens-Gerrits Merel Albers Marion De Klerk Geert-Jan 《Plant Cell, Tissue and Organ Culture》1998,52(1-2):75-77
Plant Cell, Tissue and Organ Culture (PCTOC) - 相似文献
7.
K Yamaoka S L Marion A Gallegos M R Haussler 《Biochemical and biophysical research communications》1986,139(3):1292-1298
We tested the influence of daily subcutaneous injections of 12.5 and 25 pmol of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on the growth of tumors arising from intracutaneous inoculations of athymic nude mice with rat osteogenic sarcoma cells (ROS) and human melanoma cells. Both doses of 1,25(OH)2D3 increased plasma calcium levels after 3 weeks and produced a striking enhancement in tumor weight when the mice received 1,25(OH)2D3 receptor-rich ROS17/2.8 cells. In contrast, 1,25(OH)2D3 caused no consistent effect on tumor weight in mice given G-361 melanoma cells with low receptor copy number or receptor deficient ROS 24/1 cells. Thus, 1,25(OH)2D3 stimulated tumor growth in a receptor dependent fashion, in vivo, instead of inhibiting it as predicted from the reduction of proliferation of cultured cells in the presence of 1,25(OH)2D3. 相似文献
8.
Eukaryotic 60S ribosomal subunits were studied by transient electric birefringence. Conformations of subunits in active and inactive states upon changes in magnesium concentration were compared by electric birefringence and orientational relaxation time measurements. Active subunits exhibit a positive birefringence and a relaxation time of the order of 8 microseconds. In the presence of EDTA, inactive subunits show no birefringence. When Mg2+ is reverted in the cold to its initial level, the electro-optical properties of the subunits are partially restored although the particles remain biologically inactive. 相似文献
9.
The dry weight and the crest length of the upper and lower beak, the length of the radula ribbon, the average width of the base of the six proximal and distal rachidian teeth as well as the total number of these teeth have all been related to the live body weight of octopuses between 1.1 and 4440 g. From any one of these parameters it is possible to estimate the size and approximate age of the animal. 相似文献
10.
An argument for the existence of a natural complex between protein L5 and 5 S RNA in rat liver 60-S ribosomal subunits 总被引:1,自引:0,他引:1
Electrophoresis of the 60-S ribosomal subunits from rat liver in the presence of citrate ions removes the 7 S ribonucleoprotein complex between protein L5 and 5 S RNA though this complex is not released by dialysis or by centrifugation through a sucrose cushion in the same buffer. Using acetate instead of citrate, the subunits remain intact in all cases. On the other hand, in the presence of EDTA, the complex is always released. The poly(U) directed polyphenylalanine synthesis is correlated in each case with the presence of this complex within the subunits. The melting curves of subunits which have been treated with citrate, acetate or EDTA and then taken back in the buffer in which they were stored suggest that the specific RNA-protein interactions are preserved in the presence of acetate and of citrate but not of EDTA. As a whole, the results support the interpretation that the association of protein L5 and 5 S RNA exists within the active subunits. 相似文献