全文获取类型
收费全文 | 10888篇 |
免费 | 823篇 |
国内免费 | 631篇 |
专业分类
12342篇 |
出版年
2024年 | 22篇 |
2023年 | 147篇 |
2022年 | 288篇 |
2021年 | 447篇 |
2020年 | 311篇 |
2019年 | 358篇 |
2018年 | 383篇 |
2017年 | 299篇 |
2016年 | 489篇 |
2015年 | 647篇 |
2014年 | 774篇 |
2013年 | 845篇 |
2012年 | 1004篇 |
2011年 | 921篇 |
2010年 | 566篇 |
2009年 | 500篇 |
2008年 | 586篇 |
2007年 | 547篇 |
2006年 | 461篇 |
2005年 | 417篇 |
2004年 | 366篇 |
2003年 | 350篇 |
2002年 | 318篇 |
2001年 | 139篇 |
2000年 | 138篇 |
1999年 | 117篇 |
1998年 | 85篇 |
1997年 | 83篇 |
1996年 | 66篇 |
1995年 | 57篇 |
1994年 | 63篇 |
1993年 | 50篇 |
1992年 | 62篇 |
1991年 | 55篇 |
1990年 | 51篇 |
1989年 | 38篇 |
1988年 | 26篇 |
1987年 | 18篇 |
1986年 | 32篇 |
1985年 | 22篇 |
1984年 | 29篇 |
1983年 | 11篇 |
1982年 | 16篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
W. L. Bai C. Y. Zhou Y. Ren R. H. Yin W. Q. Jiang S. J. Zhao S. C. Zhang B. L. Zhang G. B. Luo Z. H. Zhao 《Molecular biology reports》2011,38(1):471-479
The aim of the present work was to investigate single nucleotide polymorphism (SNP) of growth hormone receptor (GHR) gene exon 10, characterize the genetic variation in three Chinese indigenous goat breeds, and search for its potential association
with cashmere traits. In this study, a polymerase chain reaction-single strand conformation polymorphism (PCR–SSCP) protocol
has been developed for rapid genotyping of the GHR gene in goats. One hundred seventy-eight goats from Liaoning Cashmere (96), Inner Mongolia White Cashmere (40), and Chengdu
Grey (42) breeds in China were genotyped at GHR locus using the protocol developed. In all goat breeds investigated, a SNP in exon 10 of GHR gene has been identified by analyzing genomic DNA. The polymorphism consists of a single nucleotide substitution A → G, resulting
in two alleles named, respectively, A and G based on the nucleotide at the position. The allele A was found to be more common
in the animals investigated, and seems to be more consistent with cattle and zebu at this polymorphic site found in goats.
The Hardy–Weinberg equilibrium of genotype distributions of GHR locus was verified in Liaoning Cashmere, and Inner Mongolia White Cashmere breeds. According to the classification of polymorphism
information content (PIC), Chengdu Grey was less polymorphic than Liaoning Cashmere and Inner Mongolia White Cashmere breeds at this locus. The phylogenetic
tree of different species based on the nucleotide sequences of GHR gene exon 10 is generally in agreement with the known species relationship. No significant association was found between
the polymorphism revealed and the cashmere traits analyzed in present work. 相似文献
972.
硒对培养人胚肝细胞Ⅲ型前胶原,羟脯氨酸合成的影响 总被引:7,自引:0,他引:7
原代培养人胚肝细胞经1.156×10 ̄(-7)mol/L硒预处理4h,加入20mmol/L四氟化碳作用20h,观察硒对其Ⅲ型前胶原(PCⅢ)和羟脯氨酸(Hyp)生成的影响。结果培养液中PCⅢ水平、细胞内Hyp含量及细胞内外丙二醛(MDA)水平均降低,与未加硒对照组比较差别有显著性(P<0.01)。而硒谷腕甘肽过氧化物酶(Se-GSH-PX)活性则较对照组显著增高(P<0.001),且PCⅢ水平与Se-GSH-P_X/MDA比值呈负相关(r=-0.9156,P<0.01)。提示硒可提高Se-GSH-P_X/MDA比值,抑制脂质过氧化激发的肝细胞胶原合成。 相似文献
973.
974.
Pan Xiao Dalm Ciska Wijffels René H. Martens Dirk E. 《Applied microbiology and biotechnology》2017,101(22):8101-8113
Applied Microbiology and Biotechnology - Normally, the growth profile of a CHO cell fed-batch process can be divided into two main phases based on changes in cell concentration, being an... 相似文献
975.
Kaiqun Ren Jing Yuan Manjun Yang Xiang Gao Xiaofeng Ding Jianlin Zhou Xingwang Hu Jianguo Cao Xiyun Deng Shuanglin Xiang Jian Zhang 《PloS one》2014,9(11)
As a member of the polymerase delta-interacting protein 1 (PDIP1) gene family, potassium channel tetramerisation domain-containing 10 (KCTD10) interacts with proliferating cell nuclear antigen (PCNA) and polymerase δ, participates in DNA repair, DNA replication and cell-cycle control. In order to further investigate the physiological functions of KCTD10, we generated the KCTD10 knockout mice. The heterozygous KCTD10+/− mice were viable and fertile, while the homozygous KCTD10−/− mice showed delayed growth from E9.0, and died at approximately E10.5, which displayed severe defects in angiogenesis and heart development. Further study showed that VEGF induced the expression of KCTD10 in a time- and dose-dependent manner. Quantitative real-time PCR and western blotting results revealed that several key members in Notch signaling were up-regulated either in KCTD10-deficient embryos or in KCTD10-silenced HUVECs. Meanwhile, the endogenous immunoprecipitation (IP) analysis showed that KCTD10 interacted with Cullin3 and Notch1 simultaneously, by which mediating Notch1 proteolytic degradation. Our studies suggest that KCTD10 plays crucial roles in embryonic angiogenesis and heart development in mammalians by negatively regulating the Notch signaling pathway. 相似文献
976.
977.
Critical Role of Cys168 in Noggin Protein's Biological Function 总被引:1,自引:0,他引:1
Liu WD Feng XL Ren CP Shi JL Yang XY Zhao M Zhou L Lan K Yao KT 《Acta biochimica et biophysica Sinica》2005,37(3):181-185
Previous studies have indicated that noggin exerts its neural inducing effect by binding and antagonizing bone morphogenetic protein 4 (BMP4). In order to further clarify the relationship between the structure and the function of noggin, and elucidate the possible mechanism responsible for noggin-BMP4 interaction, we generated three noggin mutants, C168S, C174S and C197S, by using a site-directed mutagenesis method. Ectopic expression of wild-type (WT) noggin, C174S or C197S, in Xenopus animal caps (ACs) by mRNA injection converted the explants (prospective ectoderm) into neural tissue, as indicated by the neural-like morphology and expression of the neural cell adhesion molecule (NCAM) in the ACs. In contrast, ACs expressing C168S suffered an epidermal fate similar to the control caps. Similarly, among the three mutants, only C168S lost the dorsalizing function. These studies highlight the critical role played by Cys168 in noggin‘s biological activities. It probably participates in the formation of an intermolecular disulfide bridge. 相似文献
978.
Krukenberg tumor originated from stomach in female patients is common in clinical practice, but it is still uncertain whether surgical resection of ovarian metastases could improve the outcome. Some studies suggested that a certain group of patients could benefit from the resection of ovarian metastases. However, conclusions were different between studies and there was no data to illustrate if certain molecular markers were associated with patients’ survival. In this study, we analyzed the effects of resection of ovarian metastases, and investigated prognostic factors in 133 patients with ovarian metastases originated from stomach. Furthermore, we examined the expression of some cancer stem cells (CSCs) markers or related molecules in 64 ovarian metastases specimens and analyzed the correlation between these molecules and patients’ survival. We found that the median overall survival (mOS) of all 133 patients was 16 months, and “gastrectomy” and “without ascites” were two independent prognostic factors associated with longer survival. The mOS of the patients with gastrectomy was longer than that of patients had not undergone gastrectomy (19 vs. 9 months, p = 0.048). Patients without ascites survived longer than those with ascites (mOS: 21 vs. 13 months, p = 0.008). We also found that Sox2, CD44 or CD133 positive expression in ovarian metastases were risk factors correlated with poor survival, and Sox2 expression was an independent prognostic indicator. These results suggested that ovarian metastasectomy might help to prolong the survivor of some patients with Krukenberg tumor originated from stomach. Patients without ascites, and with resected or resectable primary gastric cancer lesion could get benefit from and be potential candidate for surgical treatment. The expression of Sox2 might serve as a prognostic indicator for predicting patients’ survival and be helpful for selecting patients in future. 相似文献
979.
To investigate the effect of exogenous Spermidine (Spd) and Spermine (Spm) on drought-induced damage to seedlings of Cerasus humili, relative water content (RWC), malondialdehyde content, relative electrolyte leakage, superoxide (O2 ?, SOD) generation rate, hydrogen peroxide (H2O2), endogenous polyamines (PAs), antioxidant enzymes [SOD and peroxidase (POD)] activities, PA-biosynthetic enzymes [arginine decarboxylase (ADC), ornithine decarboxylase (ODC), S-adenosylmethionine decarboxylase (SAMDC)] activities, as well as photosynthetic parameters, were measured in greenhouse cultured seedlings of C. humili. The results showed that either exogenous Spd or Spm (0.2 mM) significantly enhanced the level of RWC and prevented drought-induced lipid peroxidation. They also significantly enhanced photosynthetic capability and decreased O2 ? generation rate and H2O2 content. In addition, Spd and Spm helped to maintain SOD and POD activities in C. humili seedlings subjected to water stress, suggesting that they exerted a positive effect on antioxidant systems. The contents of endogenous free putrescine, Spd and Spm were increased to different extents in water-stressed C. humili seedlings. By the end of drought treatment (21 days) with exogenous Spd or Spm, the contents of free Spd increased by 30 and 38 %, respectively, and endogenous Spm increased by 41 and 26 %, respectively, compared with water-stressed plants. Furthermore, exogenous Spd or Spm enhanced the activities of ADC, ODC, and SAMDC. The pretreatment with Spd or Spm prevents oxidative damage induced by drought, and the protective effect of Spd was found to be greater than that of Spm. 相似文献
980.
Tekle Tafese Fida Philip Breugelmans Rob Lavigne Jan Roelof van der Meer René De Mot Pierre-Joseph Vaysse Dirk Springael 《Applied and environmental microbiology》2014,80(11):3350-3361
The aim of this study was to identify genes involved in solute and matric stress mitigation in the polycyclic aromatic hydrocarbon (PAH)-degrading Novosphingobium sp. strain LH128. The genes were identified using plasposon mutagenesis and by selection of mutants that showed impaired growth in a medium containing 450 mM NaCl as a solute stress or 10% (wt/vol) polyethylene glycol (PEG) 6000 as a matric stress. Eleven and 14 mutants showed growth impairment when exposed to solute and matric stresses, respectively. The disrupted sequences were mapped on a draft genome sequence of strain LH128, and the corresponding gene functions were predicted. None of them were shared between solute and matric stress-impacted mutants. One NaCl-affected mutant (i.e., NA7E1) with a disruption in a gene encoding a putative outer membrane protein (OpsA) was susceptible to lower NaCl concentrations than the other mutants. The growth of NA7E1 was impacted by other ions and nonionic solutes and by sodium dodecyl sulfate (SDS), suggesting that opsA is involved in osmotic stress mitigation and/or outer membrane stability in strain LH128. NA7E1 was also the only mutant that showed reduced growth and less-efficient phenanthrene degradation in soil compared to the wild type. Moreover, the survival of NA7E1 in soil decreased significantly when the moisture content was decreased but was unaffected when soluble solutes from sandy soil were removed by washing. opsA appears to be important for the survival of strain LH128 in soil, especially in the case of reduced moisture content, probably by mitigating the effects of solute stress and retaining membrane stability. 相似文献