全文获取类型
收费全文 | 3274篇 |
免费 | 180篇 |
国内免费 | 1篇 |
出版年
2023年 | 17篇 |
2022年 | 52篇 |
2021年 | 102篇 |
2020年 | 61篇 |
2019年 | 57篇 |
2018年 | 107篇 |
2017年 | 90篇 |
2016年 | 115篇 |
2015年 | 127篇 |
2014年 | 158篇 |
2013年 | 197篇 |
2012年 | 274篇 |
2011年 | 228篇 |
2010年 | 137篇 |
2009年 | 124篇 |
2008年 | 150篇 |
2007年 | 146篇 |
2006年 | 110篇 |
2005年 | 105篇 |
2004年 | 93篇 |
2003年 | 79篇 |
2002年 | 87篇 |
2001年 | 74篇 |
2000年 | 75篇 |
1999年 | 54篇 |
1998年 | 19篇 |
1997年 | 17篇 |
1996年 | 33篇 |
1995年 | 18篇 |
1994年 | 18篇 |
1993年 | 18篇 |
1992年 | 48篇 |
1991年 | 33篇 |
1990年 | 26篇 |
1989年 | 33篇 |
1988年 | 25篇 |
1987年 | 28篇 |
1986年 | 18篇 |
1985年 | 31篇 |
1984年 | 25篇 |
1982年 | 14篇 |
1981年 | 17篇 |
1980年 | 22篇 |
1979年 | 26篇 |
1978年 | 27篇 |
1977年 | 17篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1973年 | 17篇 |
1972年 | 13篇 |
排序方式: 共有3455条查询结果,搜索用时 31 毫秒
1.
Background
Substituted catechols are important precursors for large-scale synthesis of pharmaceuticals and other industrial products. Most of the reported chemical synthesis methods are expensive and insufficient at industrial level. However, biological processes for production of substituted catechols could be highly selective and suitable for industrial purposes. 相似文献2.
3.
The influence of age, weaning, season of the year and body weight on the peripheral levels of progesterone, oestradiol-17β and luteinizing hormone (LH) were studied during neonatal, perinatal and peripubertal periods in buffalo heifers. The buffalo heifers exhibited oestrus only after 30 months of age and had higher levels of LH and oestradiol-17β and a lower level of progesterone on the day of oestrus. The progesterone concentration was affected significantly (P < 0.01) by different seasons, by weaning (P < 0.05) and varied between pubertal and neonatal periods (P < 0.01), whereas the oestradiol-17β level was affected significantly (P < 0.01) by weaning and varied at different seasons and with body weight. However, the LH concentration was greater during the neonatal period than the pre- and peripubertal periods and changed significantly (P < 0.01) between groups of ages and body weights. The results suggest that increases in the levels of oestradiol-17β and progesterone after 30 months of age are probably indicative of the onset of puberty in buffalo heifers. However, a further increase in oestradiol-17β, LH, and a decrease in progesterone are essential for oestrus and cyclicity to be exhibited in buffalo heifers. 相似文献
4.
There is an urgent need for effective prophylactic measures against Mycobacterium tuberculosis (Mtb) infection, particularly given the highly variable efficacy of Bacille Calmette-Guerin (BCG), the only licensed vaccine against tuberculosis (TB). Most studies indicate that cell-mediated immune responses involving both CD4+ and CD8+ T cells are necessary for effective immunity against Mtb. Genetic vaccination induces humoral and cellular immune responses, including CD4+ and CD8+ T-cell responses, against a variety of bacterial, viral, parasitic and tumor antigens, and this strategy may therefore hold promise for the development of more effective TB vaccines. Novel formulations and delivery strategies to improve the immunogenicity of DNA-based vaccines have recently been evaluated, and have shown varying degrees of success. In the present study, we evaluated DNA-launched Venezuelan equine encephalitis replicons (Vrep) encoding a novel fusion of the mycobacterial antigens α-crystallin (Acr) and antigen 85B (Ag85B), termed Vrep-Acr/Ag85B, for their immunogenicity and protective efficacy in a murine model of pulmonary TB. Vrep-Acr/Ag85B generated antigen-specific CD4+ and CD8+ T cell responses that persisted for at least 10 wk post-immunization. Interestingly, parenterally administered Vrep-Acr/Ag85B also induced T cell responses in the lung tissues, the primary site of infection, and inhibited bacterial growth in both the lungs and spleens following aerosol challenge with Mtb. DNA-launched Vrep may, therefore, represent an effective approach to the development of gene-based vaccines against TB, particularly as components of heterologous prime-boost strategies or as BCG boosters. 相似文献
5.
Niyati Jain Christopher E. Morgan Brittany D. Rife Marco Salemi Blanton S. Tolbert 《The Journal of biological chemistry》2016,291(5):2331-2344
Splicing patterns in human immunodeficiency virus type 1 (HIV-1) are maintained through cis regulatory elements that recruit antagonistic host RNA-binding proteins. The activity of the 3′ acceptor site A7 is tightly regulated through a complex network of an intronic splicing silencer (ISS), a bipartite exonic splicing silencer (ESS3a/b), and an exonic splicing enhancer (ESE3). Because HIV-1 splicing depends on protein-RNA interactions, it is important to know the tertiary structures surrounding the splice sites. Herein, we present the NMR solution structure of the phylogenetically conserved ISS stem loop. ISS adopts a stable structure consisting of conserved UG wobble pairs, a folded 2X2 (GU/UA) internal loop, a UU bulge, and a flexible AGUGA apical loop. Calorimetric and biochemical titrations indicate that the UP1 domain of heterogeneous nuclear ribonucleoprotein A1 binds the ISS apical loop site-specifically and with nanomolar affinity. Collectively, this work provides additional insights into how HIV-1 uses a conserved RNA structure to commandeer a host RNA-binding protein. 相似文献
6.
7.
8.
A two layer model for water flux through the artery is studied using a mathematical model based on the theory for the consolidation of water saturated soils. The matrix is considered to be constituted by two layers with different permeabilities and different elastic constants and the two systems of equations are coupled with the condition of continuity of pressure, total stress, solid displacement and fluid seepage velocity at the interface. The luminal pressure is considered to be harmonic in time. Exact solutions are obtained for displacements and pressures in both the layers. For large consolidation times, large pressure gradients are found to exist near the boundaries and at the interface. The heterogeneous model may not only be useful to understand the mechanics of transport in the physiological system but it will also help the bioengineers to choose proper implant materials to design artificial vascular organs for the purpose of prosthesis. 相似文献
9.
Maintenance and stability of introduced genotypes in groundwater aquifer material. 总被引:10,自引:9,他引:1
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Three indigenous groundwater bacterial strains and Pseudomonas putida harboring plasmids TOL (pWWO) and RK2 were introduced into experimentally contaminated groundwater aquifer microcosms. Maintenance of the introduced genotypes was measured over time by colony hybridization with gene probes of various specificity. On the basis of the results of colony hybridization quantitation of the introduced organisms and genes, all introduced genotypes were stably maintained at approximately 10(5) positive hybrid colonies g-1 of aquifer microcosm material throughout an 8-week incubation period. Concomitant removal of the environmental contaminants, viz., toluene, chlorobenzene, and styrene, in both natural (uninoculated) and inoculated aquifer microcosms was also demonstrated. The results indicate that introduced catabolic plasmids, as well as indigenous organisms, can be stably maintained in groundwater aquifer material without specific selective pressure for the introduced genotypes. These results have positive implications for in situ treatment and biodegradation in contaminated aerobic groundwater aquifers. 相似文献
10.