全文获取类型
收费全文 | 4925篇 |
免费 | 270篇 |
出版年
2023年 | 37篇 |
2022年 | 63篇 |
2021年 | 118篇 |
2020年 | 96篇 |
2019年 | 110篇 |
2018年 | 103篇 |
2017年 | 106篇 |
2016年 | 141篇 |
2015年 | 207篇 |
2014年 | 194篇 |
2013年 | 267篇 |
2012年 | 462篇 |
2011年 | 1018篇 |
2010年 | 468篇 |
2009年 | 510篇 |
2008年 | 177篇 |
2007年 | 176篇 |
2006年 | 138篇 |
2005年 | 128篇 |
2004年 | 97篇 |
2003年 | 93篇 |
2002年 | 74篇 |
2001年 | 47篇 |
2000年 | 37篇 |
1999年 | 21篇 |
1998年 | 34篇 |
1997年 | 17篇 |
1996年 | 20篇 |
1995年 | 21篇 |
1994年 | 16篇 |
1993年 | 12篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 16篇 |
1985年 | 11篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 7篇 |
排序方式: 共有5195条查询结果,搜索用时 468 毫秒
31.
Elnur Babayev Chanakarn Suebthawinkul Dilan Gokyer Wendena S. Parkes Felipe Rivas Mary Ellen Pavone Adam R. Hall Michele T. Pritchard Francesca E. Duncan 《Aging cell》2023,22(11):e14004
Reproductive aging is associated with ovulatory defects. Age-related ovarian fibrosis partially contributes to this phenotype as short-term treatment with anti-fibrotic compounds improves ovulation in reproductively old mice. However, age-dependent changes that are intrinsic to the follicle may also be relevant. In this study, we used a mouse model to demonstrate that reproductive aging is associated with impaired cumulus expansion which is accompanied by altered morphokinetic behavior of cumulus cells as assessed by time-lapse microscopy. The extracellular matrix integrity of expanded cumulus–oocyte complexes is compromised with advanced age as evidenced by increased penetration of fluorescent nanoparticles in a particle exclusion assay and larger open spaces on scanning electron microscopy. Reduced hyaluronan (HA) levels, decreased expression of genes encoding HA-associated proteins (e.g., Ptx3 and Tnfaip6), and increased expression of inflammatory genes and matrix metalloproteinases underlie this loss of matrix integrity. Importantly, HA levels are decreased with age in follicular fluid of women, indicative of conserved reproductive aging mechanisms. These findings provide novel mechanistic insights into how defects in cumulus expansion contribute to age-related infertility and may serve as a target to extend reproductive longevity. 相似文献
32.
Norihiko Misawa Shigeyuki Yamano Hartmut Linden Maria R. de Felipe Mercedes Lucas Hiroshi Ikenaga Gerhard Sandmann 《The Plant journal : for cell and molecular biology》1993,4(5):833-840
Among the enzymes involved in carotenoid biosynthesis, phytoene desaturase is considered to be a rate-limiting enzyme in this pathway and is also the target of many bleaching herbicides. This enzyme shows diversity concerning its function and amino acid homology among various organisms. The phytoene desaturase gene crtl of Erwinia uredovora was expressed, the 5'-region of which was fused to the sequence for the transit peptide of a pea Rubisco small subunit, in tobacco plants under the control of the CaMV 35S promoter. This chimeric gene product was targeted into chloroplasts and processed in the transgenic plants. The production and processing of the corresponding protein could be demonstrated by Western blotting. Immunogold localization showed that the location of the gene product Crtl was preferentially in the thylakoids. A radioactive labeling study using the leaves demonstrated enhanced activity for the synthesis of β-carotene. In addition, the transgenic tobacco acquired elevated resistance to the bleaching herbicide norflurazon. 相似文献
33.
The Effects of Chilling in the Light on Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Activation in Tomato (Lycopersicon esculentum Mill.) 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Photosynthesis rate, ribulsoe-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activation state, and ribulose bisphosphate concentration were reduced after exposing tomato (Lycopersicon esculentum Mill.) plants to light at 4[deg]C for 6 h. Analysis of lysed and reconsituted chloroplasts showed that activity of the thylakoid membrane was inhibited and that Rubisco, Rubisco activase, and other soluble factors were not affected. Leaf photosynthesis rates and the ability of chilled thylakoid membranes to promote Rubisco activation recovered after 24 h at 25[deg]C. Thylakoid membranes from control tomato plants were as effective as spinach thylakoids in activating spinach Rubisco in the presence of spinach Rubisco activase. This observation is in sharp contrast to the poor ability of spinach Rubisco activase to activate tomato Rubisco (Z.-Y. Wang, G.W. Snyder, B.D. Esau, A.R. Portis, and W.L. Ogren [1992] Plant Physiol 100: 1858-1862). The ability of thylakoids from chilled tomato plants to activate Rubisco in the assay system was greatly inhibited compared to control plants. These experiments indicate that chilling tomato plants at 4[deg]C interferes with photosynthetic carbon metabolism at two sites, thioredoxin/ferredoxin reduction (G.F. Sassenrath, D.R. Ort, and A.R. Portis, Jr. [1990] Arch Biochem Biophys 282: 302-308), which limits bisphosphatase activity, and Rubisco activase, which reduces Rubisco activation state. 相似文献
34.
Peter Ort Igor A. Zalunin Victor S. Gasparov Galina G. Chestukhina Valentin M. Stepanov 《Journal of Protein Chemistry》1995,14(4):241-249
Denaturation ofBacillus thuringiensis CryIIIA-endotoxin—an insecticidal protein, active againstColeoptera larvae—in concentrated guanidine hydrochloride solutions was pursued by fluorescence and circular dichroism spectroscopy and limited proteolysis. It was found that the protein consists of two fragments that differ by their stability to denaturation by guanidine hydrochloride atpH 3. The less stable fragment corresponds to the N-terminal-helical domain limited by Leu-279; the more stable one starts with Ile-280, contains about 330 amino acid residues, and corresponds to the molecule C-terminal moiety that consist of its two-structural domains forming a superdomain.Abbreviations BT
Bacillus thuringiensis
- Gdn-HCl
guanidine hydrochloride
- PAGE
electrophoresis in polyacrylamide gel
- SDS
sodium dodecylsulfate
- CD
circular dichroism 相似文献
35.
Dinucleotide repeat polymorphism at the D4S2458 locus close to the PKD2 locus on human chromosome 4q
Miguel Viribay Dolores Tellería Eladio Velasco Felipe Moreno José L. San Millán 《Human genetics》1995,95(5):601-602
A new polymorphic CA repeat sequence was identified within the candidate region fot the autosomal dominant polycystic kidney disease type 2 (PKD2) locus. It should be a useful marker in the localization of this gene. 相似文献
36.
37.
Insensitivity of Water-Oxidation and Photosystem II Activity in Tomato to Chilling Temperatures 总被引:5,自引:4,他引:1
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Chilling tomato plants (Lycopersicon esculentum Mill. cv. Rutgers and cv. Floramerica) in the dark resulted in a sizable inhibition in the rate of light- and CO2-saturated photosynthesis. However, at low light intensity, the inhibition disappeared and the absolute quantum yield of CO2 reduction was diminished only slightly. The quantum yield of photosystem II (PSII) electron flow was 18% lower when measured in chloroplasts isolated from chilled leaves than in chloroplasts isolated from unchilled leaves. Even though the maximum rate of PSII turnover in these chloroplasts was 12% lower subsequent to chilling, it was in all cases two or more times that required to support the light- and CO2-saturated rate of photosynthesis measured in the attached leaf. The concentration of active PSII centers in chloroplasts isolated from leaves either before or after chilling was determined by measurement of the products of water oxidation from a series of saturating flashes short enough to turnover the electron transport carriers only a single time. There was no significant change in the concentration of active PSII centers due to dark chilling.
It was concluded that PSII activity and water oxidation capacity are not significantly impaired in tomato by chilling in the dark and therefore are not primary aspects of the inhibition of CO2 reduction observed in attached leaves.
相似文献38.
African swine fever virus DNA sediments in neutral sucrose density gradients as a single component with a sedimentation coefficient of 60S. In alkaline sucrose density gradients, this material shows two components with sedimentation coefficients of 85S and 95S, respectively. The sedimentation rate value of alkali-denatured virus DNA in neutral sucrose density gradients and the renaturation velocity of denatured DNA show that is reassociated much faster than expected from its genetic complexity. This behavior is compatible with the existence of interstrand cross-links in the molecule. We also present results which suggest that there are only a few such cross-links per molecule, that they are sensitive to S1 nuclease digestion, and that they are probably located next to the ends of the DNA. 相似文献
39.
Summary Two new cases of the D.O.O.R. syndrome are reported. The patients described showed most of the characteristics described by Cantwell (1975) and some others that may represent additional clinical findings of this rare syndrome. 相似文献
40.
LyM-1 is the provisional designation given to a system of murine cell-surface alloantigens which are controlled by genes closely linked to those of theMls system. Formal genetic analysis has failed to disclose separation of genes determiningMls and LyM-1 antigens, but studies of the distribution of these antigens among inbred strains shows that the LyM-1 polymorphism is not primarily responsible for the MLR activity associated with Mls differences, and suggests that LyM-1 and Mls substances are products of genes at closely linked, but probably separate loci. Absorption analysis shows that strains whose cells react with anti-LyM-1.2 can be divided into at least two classes on the basis of the efficiency with which their cells remove anti-LyM-1.2 antibodies. This provides evidence for the existence of two LyM-1 alleles in addition to the one(s) possessed by nonreactive mouse strains. 相似文献