全文获取类型
收费全文 | 3795篇 |
免费 | 296篇 |
出版年
2021年 | 35篇 |
2020年 | 25篇 |
2019年 | 27篇 |
2018年 | 39篇 |
2017年 | 47篇 |
2016年 | 71篇 |
2015年 | 98篇 |
2014年 | 131篇 |
2013年 | 223篇 |
2012年 | 172篇 |
2011年 | 172篇 |
2010年 | 113篇 |
2009年 | 120篇 |
2008年 | 180篇 |
2007年 | 165篇 |
2006年 | 200篇 |
2005年 | 169篇 |
2004年 | 155篇 |
2003年 | 151篇 |
2002年 | 166篇 |
2001年 | 101篇 |
2000年 | 113篇 |
1999年 | 109篇 |
1998年 | 67篇 |
1997年 | 61篇 |
1996年 | 41篇 |
1995年 | 52篇 |
1994年 | 59篇 |
1993年 | 38篇 |
1992年 | 68篇 |
1991年 | 61篇 |
1990年 | 74篇 |
1989年 | 69篇 |
1988年 | 63篇 |
1987年 | 53篇 |
1986年 | 55篇 |
1985年 | 42篇 |
1984年 | 38篇 |
1983年 | 33篇 |
1982年 | 47篇 |
1981年 | 40篇 |
1980年 | 28篇 |
1979年 | 49篇 |
1978年 | 36篇 |
1977年 | 23篇 |
1976年 | 29篇 |
1975年 | 26篇 |
1974年 | 33篇 |
1973年 | 24篇 |
1972年 | 15篇 |
排序方式: 共有4091条查询结果,搜索用时 31 毫秒
1.
Silk fibroin with the alanyl carboxyl carbon enriched with 13C was obtained by giving a diet containing 13C-enriched alanine to the larvae of Bombyx mori and Antheraea pernyi at the fifth instar. Sericin-free fibroin fibers were prepared from cocoons, and gut was made from the liquid silk in the gland. The final 13C content was about 13%. Cross polarization/magic angle sample spinning spectra at 25 MHz and 75 MHz were measured for each sample at different orientations. Spectra were simulated using the principal values and orientations of the shielding tensor in the alanine crystal. The results indicate that the beta-structure of the fibroin may be a little more flattened than the typical pleated sheet beta-structure. 相似文献
2.
When rats received glucagon or insulin every 2 h after partial hepatectomy (Hx), hepatic putrescine content was increased above control levels at 6 and 12 h, respectively. When the two hormones were combined, the increased levels were additive. Hepatic ornithine decarboxylase activity was above control levels at 12 h after insulin treatment. Hepatic spermidine N1-acetyltransferase activity was enhanced at 6 h only when glucagon was dosed. Putrescine administration from 0 to 4 h or from 6 to 10 h increased hepatic DNA synthesis to similar levels 22 h after Hx. These results suggest that glucagon and insulin additively stimulate hepatic putrescine production after Hx. This may explain the cooperative stimulation of liver regeneration by both hormones. 相似文献
3.
Adenylate and guanylate cyclase activities were confirmed in crude homogenates from rat peritoneal mast cells. Both enzyme activities were associated with the 105, 000 X g particulate fractions, but not detected in the supernatant fractions. The optimal pH for both cyclase activities was 8.2. Mn++ was essentially required for guanylate cylcase activity, while adenylate cyclase activity was observed in the presence of either Mg++ or Mn++. The apparent Km values of adenylate cyclase for Mn++-ATP and Mg++-ATP were 160 μM and 340 μM, respectively, whereas the value of guanylate cyclase for Mn++-GTP was 100 μM. Adenylate cyclase was activated by 10 mM NaF. However, both adenylate and guanylate cyclase activities were neither stimulated nor inhibited by the addition of various kinds of agents which stimulate or inhibit the release of histamine from mast cells. 相似文献
4.
Yusuke Nakamura Michio Ogawa Takahiro Nishide Mitsuru Emi Goro Kosaki Seiichi Himeno Kenichi Matsubara 《Gene》1984,28(2):263-270
The nucleotide sequences of the cloned human salivary and pancreatic α-amylase cDNAs correspond to the continuous mRNA sequences of 1768 and 1566 nucleotides, respectively. These include all of the amino acid coding regions. Salivary cDNA contains 200 bp in the 5′-noncoding region and 32 in the 3′-noncoding region. Pancreatic cDNA contains 3 and 27 bp of 5′- and 3′-noncoding regions, respectively. The nucleotide sequence humology of the two cDNAs is 96% in the coding region, and the predicted amino acid sequences are 94% homologous.Comparison of the sequences of human α-amylase cDNAs with those previously obtained for mouse α-amylase genes (Hagenbuchle et al., 1980; Schibler et al., 1982) showed the possibility of gene conversion between the two genes of human α-amylase. 相似文献
5.
6.
The activities of glutamic oxaloacetic transaminase and Ca++ ion-activated ATPase of muscle in the adult rats fed a protein-free diet for 8, 16 and 24 days were measured in order to clarify their metabolic responses with respect to reserve proteins. It was found that these enzyme activities, or presumably their enzyme proteins, decreased at the stage as early as the 8th day of protein depletion following the same pattern as seen in reserve proteins. Their responses, particularly those in unit activity, were somewhat different from each other. The metabolic significance of those responses was discussed in relation to protein nutrition. 相似文献
7.
8.
Toshiyuki Hamaoka Yasuyuki Takai Atsushi Kosugi Yumiko Mizushima Junko Shima Tsuneo Kusama Hiromi Fujiwara 《Cancer immunology, immunotherapy : CII》1985,20(3):183-188
Summary A new haptenic compound, a muramyl dipeptide (MDP) derivative (designated as L4-MDP-ONB) cross-reactive with Bacillus Calmette Guerin (BCG) was synthesized. The cross-reactivity of L4-MDP hapten to BCG was demonstrated from the following evidence; (a) lymph node cells from BCG-primed C3H/HeN mice exhibited appreciable L4-MDP-specific proliferative responses to the in vitro stimulation of L4-MDP-modified syngeneic cells (L4-MDP-self); (b) inoculation of L4-MDP-self into footpads of BCG-primed C3H/HeN mice elicited ample delayed type-hypersensitivity (DTH) responses in vivo as measured by footpad swelling; and (c) BCG-primed mice contained L4-MDP-reactive helper T cell activity which functions to augment the generation of effector T cell responses to cell surface antigens. This crossreactivity between L4-MDP hapten and BCG as measured by the helper T cell activity was applied to enhanced induction of tumor-specific immunity. When BCG-primed C3H/HeN mice were immunized with L4-MDP-modified syngeneic X5563 tumor cells, these mice could generate augmented tumor-specific in vivo protective (tumor neutralizing) immunity as well as in vitro cytotoxic T cell responses. These results indicate the effectiveness of L4-MDP hapten in augmenting tumor-specific immunity. The present approach is discussed in the context of potential advantages of this new hapten for its future application to clinical tumor systems. 相似文献
9.
10.
Feedbacks between nutrient cycling and vegetation predict plant species coexistence and invasion 总被引:5,自引:0,他引:5
To investigate the role of species‐specific litter decomposability in determining plant community structure, we constructed a theoretical model of the codevelopmental dynamics of soil and vegetation. This model incorporates feedback between vegetation and soil. Vegetation changes the nutrient conditions of soil by affecting mineralization processes; soil, in turn, has an impact on plant community structure. The model shows that species‐level traits (decomposability, reproductive and competitive abilities) determine whether litter feedback effects are positive or negative. The feedback determines community‐level properties, such as species composition and community stability against invasion. The model predicts that positive feedback may generate multiple alternative steady states of the plant community, which differ in species richness or community composition. In such cases, the realized state is determined by initial abundance of co‐occurring species. Further, the model shows that the importance of species‐level traits depends on environmental conditions such as system fertility. 相似文献