全文获取类型
收费全文 | 2937篇 |
免费 | 303篇 |
国内免费 | 3篇 |
出版年
2021年 | 28篇 |
2020年 | 20篇 |
2019年 | 23篇 |
2018年 | 22篇 |
2017年 | 25篇 |
2016年 | 73篇 |
2015年 | 138篇 |
2014年 | 130篇 |
2013年 | 171篇 |
2012年 | 206篇 |
2011年 | 212篇 |
2010年 | 109篇 |
2009年 | 124篇 |
2008年 | 164篇 |
2007年 | 185篇 |
2006年 | 174篇 |
2005年 | 168篇 |
2004年 | 164篇 |
2003年 | 166篇 |
2002年 | 146篇 |
2001年 | 31篇 |
2000年 | 37篇 |
1999年 | 45篇 |
1998年 | 37篇 |
1997年 | 33篇 |
1996年 | 32篇 |
1995年 | 25篇 |
1994年 | 25篇 |
1993年 | 18篇 |
1992年 | 31篇 |
1991年 | 26篇 |
1990年 | 31篇 |
1989年 | 24篇 |
1988年 | 20篇 |
1987年 | 34篇 |
1986年 | 23篇 |
1985年 | 27篇 |
1984年 | 23篇 |
1983年 | 23篇 |
1982年 | 30篇 |
1981年 | 23篇 |
1980年 | 18篇 |
1979年 | 18篇 |
1976年 | 10篇 |
1974年 | 16篇 |
1973年 | 13篇 |
1972年 | 12篇 |
1971年 | 15篇 |
1970年 | 9篇 |
1969年 | 12篇 |
排序方式: 共有3243条查询结果,搜索用时 0 毫秒
1.
Seed and leaf extracts ofMammea americana (mamey apple) have a historical use as a biopesticide with the active components previously characterized. We reexamined the utility of this natural bioinsecticide in light of existing sources of material as a by-product of the fruit processing industry. Our results addDiabrotica virgifera virgifera andTrichoplusia ni to the list of insects which are susceptible to the insecticidal ingredients ofM. americana and confirms earlier reports of activity againstBlatella germanica, Periplaneta americana, andPlutella xylostella. We report LD5Os for crude hexane extracts ofM. americana leaves and seeds againstT. ni. These materials represent renewable sources of bioinsecticides for agriculture, and should regenerate interest in coumarin-type compounds for novel pesticidal action. 相似文献
2.
3.
4.
5.
C Mapp J Hartiala O L Frick R L Shields W M Gold 《Journal of applied physiology》1986,61(4):1467-1474
The relationship between airway responsiveness to inhaled antigen and histamine, immunologic release of lung histamine, immunologic responsiveness of skin, and specific immunoglobulin E (IgE) antibodies were examined in 11 inbred allergic dogs immunized with extracts of ragweed and grass and 5 nonimmunized control dogs from the same colony. Airway responsiveness to antigen and histamine was characterized by the doses that increased the airflow resistance of the total respiratory system to twice the control values (ED200). Highly significant correlations were found between airway responsiveness and cutaneous responsiveness to antigen and other immunologic characteristics (e.g., IgE and histamine released from lung by inhaled antigen) in all dogs. In ragweed-sensitized dogs, there was an inverse correlation between immunologic responsiveness (reflected by the cutaneous response to antigen and histamine released from lung by inhaled antigen) and nonimmunologic responsiveness of airways (histamine ED200: r = 0.73, P less than 0.05 and r = 0.75, P less than 0.01, respectively). Antigen ED200 was also correlated with histamine release from lung after antigen inhalation (r = 0.74; P less than 0.01). We conclude that airway reactions to inhaled antigen in allergic dogs are dependent not only on immunologic factors but also on the degree of nonimmunologic airway responsiveness to histamine and that these factors are correlated inversely. 相似文献
6.
7.
Neide Vieira Margarida Casal Björn Johansson Donna M. MacCallum Alistair J.P. Brown Sandra Paiva 《Molecular microbiology》2010,75(6):1337-1354
The major fungal pathogen Candida albicans has the metabolic flexibility to assimilate a wide range of nutrients in its human host. Previous studies have suggested that C. albicans can encounter glucose‐poor microenvironments during infection and that the ability to use alternative non‐fermentable carbon sources contributes to its virulence. JEN1 encodes a monocarboxylate transporter in C. albicans and we show that its paralogue, JEN2, encodes a novel dicarboxylate plasma membrane transporter, subjected to glucose repression. A strain deleted in both genes lost the ability to transport lactic, malic and succinic acids by a mediated mechanism and it displayed a growth defect on these substrates. Although no significant morphogenetic or virulence defects were found in the double mutant strain, both JEN1 and JEN2 were strongly induced during infection. Jen1‐GFP (green fluorescent protein) and Jen2‐GFP were upregulated following the phagocytosis of C. albicans cells by neutrophils and macrophages, displaying similar behaviour to an Icl1‐GFP fusion. In the murine model of systemic candidiasis approximately 20–25% of C. albicans cells infecting the kidney expressed Jen1‐GFP and Jen2‐GFP. Our data suggest that Jen1 and Jen2 are expressed in glucose‐poor niches within the host, and that these short‐chain carboxylic acid transporters may be important in the early stages of infection. 相似文献
8.
Cell-free processing and segregation of insulin precursors 总被引:3,自引:0,他引:3
The biosynthesis, segregation, and processing of preproinsulin (116 amino acids) was investigated to determine the mechanism(s) by which it is translocated across the endoplasmic reticulum membrane. Islet mRNA was translated in the wheat germ cell-free system, and at various times during preproinsulin synthesis, puromycin was added, followed by addition of microsomal membranes. Neither processing of preproinsulin nor translocation of proinsulin into microsomal membranes occurred in the presence of puromycin. Synchronization of preproinsulin translation by addition of 7-methylguanosine 5'-phosphate enabled the timing of preproinsulin synthesis and proinsulin (91 amino acids) segregation into microsomal membranes to be determined. Membrane binding occurs when about 60 amino acids have been polymerized, i.e. prior to the completion of the polypeptide chain. The binding of signal recognition particle to the nascent signal is demonstrated to be an absolute requirement for translocation and processing of preproinsulin. The results indicate that segregation and processing of preproinsulin are co-translational events; no evidence for a post-translational mechanism was found. Furthermore, this work, together with similar studies, suggests that presecretory polypeptides must be synthesized as part of a precursor with a minimum size of 60-80 amino acids in order to effect membrane binding and translocation of the polypeptide chain within the intracisternal space of the endoplasmic reticulum. 相似文献
9.
10.
Schizophrenia: geneticism and environmentalism 总被引:1,自引:0,他引:1