全文获取类型
收费全文 | 17643篇 |
免费 | 1068篇 |
国内免费 | 3篇 |
出版年
2023年 | 110篇 |
2022年 | 200篇 |
2021年 | 459篇 |
2020年 | 375篇 |
2019年 | 394篇 |
2018年 | 462篇 |
2017年 | 443篇 |
2016年 | 647篇 |
2015年 | 977篇 |
2014年 | 1032篇 |
2013年 | 1214篇 |
2012年 | 1519篇 |
2011年 | 1343篇 |
2010年 | 874篇 |
2009年 | 800篇 |
2008年 | 1091篇 |
2007年 | 1013篇 |
2006年 | 941篇 |
2005年 | 873篇 |
2004年 | 834篇 |
2003年 | 727篇 |
2002年 | 661篇 |
2001年 | 147篇 |
2000年 | 98篇 |
1999年 | 135篇 |
1998年 | 147篇 |
1997年 | 125篇 |
1996年 | 114篇 |
1995年 | 95篇 |
1994年 | 93篇 |
1993年 | 59篇 |
1992年 | 59篇 |
1991年 | 62篇 |
1990年 | 58篇 |
1989年 | 37篇 |
1988年 | 38篇 |
1987年 | 26篇 |
1986年 | 22篇 |
1985年 | 42篇 |
1984年 | 62篇 |
1983年 | 23篇 |
1982年 | 30篇 |
1981年 | 28篇 |
1980年 | 29篇 |
1979年 | 20篇 |
1978年 | 23篇 |
1977年 | 21篇 |
1976年 | 18篇 |
1975年 | 19篇 |
1969年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
Pieri Pde C Pereira DH Glina S Hallak J McElreavey K Moreira-Filho CA 《Genetic testing》2002,6(3):185-194
PCR-based screening of microdeletions in the azoospermic factor (AZF) on the Yq chromosome is an accepted means of identifying a common genetic cause of male infertility, responsible for 5-15% of cases associated with a low sperm count (=5 x 10(6) sptz/ml). Based on an extensive analysis of the literature, we have established a cost-effective preliminary PCR-based diagnostic screening test, with a set of six pairs of primers ("set-of-6") that have the capability of detecting up to 95% of the Y microdeletion cases already published. These primers are: sY84 in AZFa, sY114, sY129, sY143 in AZFb, and sY149, sY254 in AZFc. Initially, the set-of-6 was tested with 13 other pairs of primers covering the three AZF subregions. A sample of 114 infertile men was tested and 10 (8.8%) microdeletions were found, 3 of which were among the 26 (11.5%) idiopathic azoospermic men. These results showed that all detected microdeletions would be identified using the set-of-6 only. Another sample of 34 patients was subsequently tested using the set-of-6 and 3 (8.8%) microdeletions were found in this group. A comparison of our results with those reported in the literature showed similar microdeletion detection frequencies, demonstrating that the set-of-6 primers provides a reliable, simple and cost-effective way of detecting AZF deletions. 相似文献
922.
Generation of histocompatible tissues using nuclear transplantation 总被引:27,自引:0,他引:27
923.
Kumar V Carlson JE Ohgi KA Edwards TA Rose DW Escalante CR Rosenfeld MG Aggarwal AK 《Molecular cell》2002,9(4):857-869
The Lcd1p/Mec1p complex is crucial for normal S phase progression and for signaling DNA damage. We show that Lcd1p/Ddc2p and Mec1p in cell extracts bind to DNA ends. Although Lcd1p binds DNA independently of Mec1p, recruitment of Mec1p to DNA requires Lcd1p. DNA binding by Lcd1p is also independent of Rad9p, Rad17p, and Rad24p. Recombinant Lcd1p binds DNA, and this is impaired by Lcd1p mutations that abrogate its in vivo functions. Furthermore, Mec1p is recruited to cdc13-induced DNA damage and HO endonuclease-induced double-strand breaks in vivo. This requires Lcd1p, and recruitment of Lcd1p/Mec1p to cdc13-induced damage is abolished by Lcd1p mutations that abrogate its in vivo functions. Recruitment of Lcd1p to these lesions is independent of Mec1p and Rad9p/Rad24p. Thus, recruitment of Mec1p to DNA lesions by Lcd1p is crucial for the DNA damage response. 相似文献
924.
Population structure in the endangered Blanca Cacereña bovine breed demonstrated by RAPD analyses 总被引:1,自引:0,他引:1
Parejo JC Padilla JA Rabasco A Sansinforiano ME Martinez-Trancón M 《Genes & genetic systems》2002,77(1):51-58
RAPD analyses have been used to determine the genetic diversity and the population structure of the endangered Blanca Cacere?a bovine breed. Genetic variability was evaluated on the basis of 1048 loci produced by 71 primers. RAPD produced a number of polymorphic loci (30.44%), and it has been proved to be a useful method for evaluating polymorphisms in this breed. The dendrograms based on simililarity indexes and on Nei's genetic distances between 60 animals and the value of genetic differentiation among subpopulations (F(ST)) showed a clear population substructure defined by herds and a scarce genetic flow among herds. Analysis of molecular variance (AMOVA) showed that 32.4% of the total variance was due to differences among herds and confirmed the clustering found. The results of the present study allow us to plan more adequate mating in order to maintain the genetic diversity and to improve the efficiency of conservation for the Blanca Cacere?a bovine breed. 相似文献
925.
Cordova CA Siqueira IR Netto CA Yunes RA Volpato AM Cechinel Filho V Curi-Pedrosa R Creczynski-Pasa TB 《Redox report : communications in free radical research》2002,7(2):95-102
Calendula officinalis (marigold) has many pharmacological properties. It is used for the treatment of skin disorders, pain and also as a bactericide, antiseptic and anti-inflammatory. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are known to participate in the pathogenesis of various human diseases and may be involved in the conditions which C. officinalis is used to treat. The aim of this study was to investigate the relationship between the beneficial properties of this plant and its antioxidant action. The butanolic fraction (BF) was studied because it is non-cytotoxic and is rich in a variety of bioactive metabolites including flavonoids and terpenoids. Superoxide radicals (O(2)(*-)) and hydroxyl radicals (HO(*)) are observed in decreasing concentrations in the presence of increasing concentrations of BF with IC(50) values of 1.0 +/- 0.09 mg/ml and 0.5 +/- 0.02 mg/ml, respectively, suggesting a possible free radical scavenging effect. Lipid peroxidation in liver microsomes induced by Fe(2+)/ascorbate was 100% inhibited by 0.5 mg/ml of BF (IC(50) = 0.15 mg/ml). Its total reactive antioxidant potential (TRAP) (in microM Trolox equivalents) was 368.14 +/- 23.03 and its total antioxidant reactivity (TAR) was calculated to be 249.19 +/- 14.5 microM. The results obtained suggest that the butanolic fraction of C. officinalis possesses a significant free radical scavenging and antioxidant activity and that the proposed therapeutic efficacy of this plant could be due, in part, to these properties. 相似文献
926.
Fradera X De La Cruz X Silva CH Gelpí JL Luque FJ Orozco M 《Bioinformatics (Oxford, England)》2002,18(7):939-948
Classical molecular interaction potentials, in conjunction with other theoretical techniques, are used to analyze the dependence of the binding sites of representative proteins on the bound ligand. It is found that the ligand bound introduces in general small structural perturbations at the binding site of the protein. However, such small structural changes can lead to important alterations in the recognition pattern of the protein. The impact of these findings in docking procedures is discussed. 相似文献
927.
Hypotrich ciliates present a macronuclear genome consisting of gene-sized instead of chromosome-sized DNA molecules. Exploiting this unique eukaryotic genome feature, we introduce, for the first time in ciliates, a rapid and easy PCR method using telomeric primers to isolate small complete macronuclear DNA molecules or minichromosomes. Two presumably abundant macronuclear DNA molecules, containing ribosomal genes, were amplified from the Oxytricha (Sterkiella) nova complete genome after using this method, and then were cloned and sequenced. The 5S rDNA sequence of O. (S.) nova is the third one reported among hypotrich ciliates; its primary and secondary structure is compared with other eukaryotic 5S rRNAs. The ribosomal protein S26 gene is the first one reported among ciliates. This "End-End-PCR" method might be useful to obtain similar gene-sized macronuclear molecules from other hypotrich ciliates, and, therefore, to increase our knowledge on ribosomal genes in these eukaryotic microorganisms. 相似文献
928.
Martins OG Pesty A Gouveia-Oliveira A Cidadão AJ Plancha CE Lefevre B 《Zygote (Cambridge, England)》2002,10(1):59-64
Calcium signalling is involved in important events in oocytes, such as meiotic competence acquisition. We have previously demonstrated the positive influence of animal age and gonadotropin stimulation in vivo regarding the ability of oocytes recovered from preantral follicles to exhibit calcium spikes. In the present work we determined whether preantral follicle development in vitro also allows oocytes to acquire calcium signalling activity. We also aimed to verify the influence of animal age, FSH + LH and/or insulin on oocyte calcium spike acquisition during preantral follicle culture. Early preantral follicles were isolated from 12-day-old and 1- to 3-month-old F1 hybrid mice and cultured individually for either 2 or 6 days. At the end of the culture period the oocytes were processed for calcium imaging by confocal microscopy. We show that oocytes recovered from cultured preantral follicles exhibit variable calcium spike activity rates, depending on animal age, culture duration and hormonal supplementation. Oocytes recovered from adult animals continue to exhibit calcium spikes, and those recovered from juveniles acquire that activity after culture. Insulin and gonadotropins in combination account for an early and maintained inhibitory effect on calcium signalling acquisition by oocytes. Insulin alone also leads to an early inhibitory effect, which, however, disappears with longer culture periods. Contrary to the complex in vivo situation, the acquisition of calcium signalling by oocytes in a controlled in vitro environment does not seem to be dependent on gonadotropins alone. 相似文献
929.
930.
Wah DA Fernández-Tornero C Sanz L Romero A Calvete JJ 《Structure (London, England : 1993)》2002,10(4):505-514
Bovine seminal plasma PDC-109 binds to sperm surface choline lipids and promotes sperm capacitation by stimulating the efflux of cholesterol and phospholipids. The structure of PDC-109 with bound phosphorylcholine was solved using MAD data of a single platinum site. Its two globular (40 x 50 x 20 A(3)) Fn2 domains are linked and clustered by a short polypeptide. The choline binding sites lie at the same face of the molecule. Phosphorylcholine binds to the Fn2 domains through a cation-pi interaction between the quaternary ammonium group and a core tryptophan, plus hydrogen bonding between hydroxyls of exposed tyrosines and the phosphate group. The structure of the PDC-109-oPC complex provides a structural ground for the sperm membrane-coating mechanism underlying PDC-109-induced capacitation. 相似文献