全文获取类型
收费全文 | 8700篇 |
免费 | 491篇 |
国内免费 | 6篇 |
出版年
2023年 | 76篇 |
2022年 | 124篇 |
2021年 | 254篇 |
2020年 | 151篇 |
2019年 | 168篇 |
2018年 | 236篇 |
2017年 | 214篇 |
2016年 | 275篇 |
2015年 | 356篇 |
2014年 | 411篇 |
2013年 | 573篇 |
2012年 | 580篇 |
2011年 | 559篇 |
2010年 | 344篇 |
2009年 | 279篇 |
2008年 | 391篇 |
2007年 | 349篇 |
2006年 | 337篇 |
2005年 | 334篇 |
2004年 | 275篇 |
2003年 | 224篇 |
2002年 | 231篇 |
2001年 | 201篇 |
2000年 | 178篇 |
1999年 | 164篇 |
1998年 | 60篇 |
1997年 | 56篇 |
1996年 | 65篇 |
1995年 | 52篇 |
1994年 | 59篇 |
1993年 | 37篇 |
1992年 | 117篇 |
1991年 | 117篇 |
1990年 | 88篇 |
1989年 | 95篇 |
1988年 | 88篇 |
1987年 | 90篇 |
1986年 | 87篇 |
1985年 | 92篇 |
1984年 | 82篇 |
1983年 | 50篇 |
1982年 | 48篇 |
1981年 | 42篇 |
1980年 | 48篇 |
1979年 | 78篇 |
1978年 | 58篇 |
1977年 | 49篇 |
1976年 | 42篇 |
1974年 | 39篇 |
1973年 | 44篇 |
排序方式: 共有9197条查询结果,搜索用时 15 毫秒
11.
Shiva K. Sharma Madho S. Bisht Maharaj K. Pandit 《Plant Systematics and Evolution》2010,287(1-2):29-36
In higher plants, synaptic mutation-associated gametic abnormalities are reported mostly in crop plants, but studies have rarely focused on the natural plant populations. This is particularly so in threatened herbaceous perennials, some of which are known to suffer from loss of sexual reproduction driven by the genetic mutations. Cytological investigations of Panax species, viz. P. sikkimensis, P. sokpayensis and P. bipinnatifidus, revealed that all the species were diploid with 2n = 24 chromosomes. Natural occurrence of synaptic mutation was recorded in Panax sikkimensis in the Kalep population of North Sikkim, India. We recorded that 86.03% of pollen mother cells (PMCs) lacked bivalent formation and had 24 distinct univalents at prophase I in the mutant plants of P. sikkimensis. We found a significantly lower mean number of chiasmata per cell (0.31 ± 0.91; t test = 38.24, P < 0.001) in the mutant plants as compared to the normal plants (21.04 ± 4.56). The chromosomal associations in the PMCs of the synaptic mutants ranged from 25% bivalents and 75% univalents to 100% univalents at diplotene/diakinesis. The unequal distribution of chromosomes at anaphase I and II resulted in the formation of microspores and microcytes of differing sizes. The pollen stainability test in the mutant population of P. sikkimensis revealed very low (0.12%) pollen fertility reflecting the consequences of synaptic mutation. Synaptic mutation in the herbaceous perennial P. sikkimensis was considered to be responsible for the male sterility in the species. 相似文献
12.
13.
Experimental evidence suggests that proteins adsorbed to hydrophobic surfaces at low coverages are stabilized relative to the bulk. For larger coverages, proteins unfold and form β-sheets. We performed computer simulations on model proteins and found that: 1), For weakly adsorbing surfaces, unfolded conformations lose more entropy upon adsorption than folded ones. 2), The melting temperature, both in the bulk and at surfaces, decreases with increasing protein concentration because of favorable interprotein interactions. 3), Proteins in the bulk show large unfolding free energy barriers; this barrier decreases at stronger adsorbing surfaces. We conjecture that typical experimental temperatures appear to be below the bulk melting temperature for a single protein, but above the melting temperature for concentrated protein solutions. Purely thermodynamic factors then explain protein stabilization on adsorption at low concentrations. However, both thermodynamic and kinetic factors are important at higher concentrations. Thus, proteins in the bulk do not denature with increasing concentration due to large kinetic barriers, even though the aggregated state is thermodynamically preferred. However, they readily unfold upon adsorption, with the surface acting as a heterogeneous catalyst. The thermal behavior of proteins adsorbed to hydrophobic surfaces thus appears to follow behavior independent of their chemical specificity. 相似文献
14.
A comparison of liquid-holding recovery and photoreactivation in halophilic and non-halophilic bacteria 总被引:2,自引:0,他引:2
The ability of the extreme halophile Halobacterium cutirubrum to recover from the effects of ultraviolet radiation during liquid holding in the dark in non-nutrient medium has been compared with that of (i) a moderately halophilic bacterium (NRC 41227) and (ii) Escherichia coli B. The photoreactivabilities of all three bacteria have also been studied. The extreme halophile was incapable of liquid-holding recovery in these conditions, in marked contrast to both E. coli B and the moderate halophile, and also failed to recover when held in nutrient medium in the dark. These results strongly support the hypothesis that H. cutirubrum lacks DNA excision repair. It was also found that ultraviolet-irradiated H. cutirubrum could be almost completely photoreactivated from any level of survival in the range 10(-4)-80%, provided exposure to visible light was not delayed, whereas the moderate halophile resembled E. coli B and had a comparatively limited capacity for photoreactivation. 相似文献
15.
H K Sharma H R Prasanna R S Lane M Rothstein 《Archives of biochemistry and biophysics》1979,194(1):275-282
The rates of synthesis and degradation of enolase and total soluble proteins slow with age in the free-living nematode, Turbatrix aceti. The half-lives are 73 and 58 h for soluble protein and enolase, respectively, in young organisms (5 days old). The respective figures are 163 and 161 h for old organisms (22–30 days old). Similar slowing of protein turnover occurs when the organisms are aged by a repeated screening procedure which avoids the use of fluorodeoxyuridine, an inhibitor of DNA synthesis normally added to aging cultures to obtain synchrony. The results support the idea that slowed protein turnover may be responsible for the formation of altered enzymes in old organisms. 相似文献
16.
R K Sharma 《Biochemical and biophysical research communications》1991,181(1):493-497
Polyclonal antibodies raised against bovine heart high molecular weight calmodulin-binding protein were used to study the distribution of this protein in diverse bovine tissues. The high molecular weight calmodulin-binding protein, in addition to bovine heart, is also present in lung and brain at much lower levels, but not in skeletal muscle, spleen, kidney or uterus. 相似文献
17.
18.
Pancreatic islets of Langerhans consist of endocrine cells, primarily α, β and δ cells, which secrete glucagon, insulin, and somatostatin, respectively, to regulate plasma glucose. β cells form irregular locally connected clusters within islets that act in concert to secrete insulin upon glucose stimulation. Due to the central functional significance of this local connectivity in the placement of β cells in an islet, it is important to characterize it quantitatively. However, quantification of the seemingly stochastic cytoarchitecture of β cells in an islet requires mathematical methods that can capture topological connectivity in the entire β-cell population in an islet. Graph theory provides such a framework. Using large-scale imaging data for thousands of islets containing hundreds of thousands of cells in human organ donor pancreata, we show that quantitative graph characteristics differ between control and type 2 diabetic islets. Further insight into the processes that shape and maintain this architecture is obtained by formulating a stochastic theory of β-cell rearrangement in whole islets, just as the normal equilibrium distribution of the Ornstein-Uhlenbeck process can be viewed as the result of the interplay between a random walk and a linear restoring force. Requiring that rearrangements maintain the observed quantitative topological graph characteristics strongly constrained possible processes. Our results suggest that β-cell rearrangement is dependent on its connectivity in order to maintain an optimal cluster size in both normal and T2D islets. 相似文献
19.
Jyotsana Prakash Rakesh Sharma Subhasree Ray Shikha Koul Vipin Chandra Kalia 《Indian journal of microbiology》2018,58(2):127-137
Wastewaters are a rich source of nutrients for microorganisms. However, if left unattended the biodegradation may lead to severe environmental hazards. The wastewaters can thus be utilized for the production of various value added products including bioenergy (H2 and CH4). A number of studies have reported utilization of various wastewaters for energy production. Depending on the nature of the wastewater, different reactor configurations, wastewater and inoculum pretreatments, co-substrate utilizations along with other process parameters have been studied for efficient product formation. Only a few studies have reported sequential utilization of wastewaters for H2 and CH4 production despite its huge potential for complete waste degradation. 相似文献
20.
K Muralidhar T Rajendrakumar H P Sharma 《Indian journal of biochemistry & biophysics》1992,29(2):168-172
Lutropin (LH-1) from water buffaloes has been shown to exhibit microheterogeneity in the N-terminal amino-acid sequence of its alpha-subunit. The beta-subunit did not exhibit such microheterogeneity. Another protocol of purification yielded a preparation of buffalo LH (bu LH-2) different from the buffalo LH-1 in certain physico-chemical properties like ease of dissociation into subunits, sugar composition, isoelectric point, and elution profile on S-200. Data appear to indicate the presence of more than one form of buffalo lutropin. 相似文献