全文获取类型
收费全文 | 42070篇 |
免费 | 3362篇 |
国内免费 | 3546篇 |
专业分类
48978篇 |
出版年
2024年 | 116篇 |
2023年 | 575篇 |
2022年 | 1322篇 |
2021年 | 2326篇 |
2020年 | 1500篇 |
2019年 | 1903篇 |
2018年 | 1908篇 |
2017年 | 1328篇 |
2016年 | 1798篇 |
2015年 | 2642篇 |
2014年 | 3099篇 |
2013年 | 3331篇 |
2012年 | 3896篇 |
2011年 | 3462篇 |
2010年 | 2163篇 |
2009年 | 1789篇 |
2008年 | 2162篇 |
2007年 | 1888篇 |
2006年 | 1733篇 |
2005年 | 1410篇 |
2004年 | 1133篇 |
2003年 | 999篇 |
2002年 | 844篇 |
2001年 | 694篇 |
2000年 | 612篇 |
1999年 | 648篇 |
1998年 | 375篇 |
1997年 | 385篇 |
1996年 | 358篇 |
1995年 | 326篇 |
1994年 | 341篇 |
1993年 | 269篇 |
1992年 | 317篇 |
1991年 | 255篇 |
1990年 | 221篇 |
1989年 | 197篇 |
1988年 | 134篇 |
1987年 | 107篇 |
1986年 | 94篇 |
1985年 | 92篇 |
1984年 | 61篇 |
1983年 | 59篇 |
1982年 | 36篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 13篇 |
1978年 | 4篇 |
1973年 | 4篇 |
1969年 | 4篇 |
1966年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
961.
962.
The availability of numerous universal markers and suitable phylogenetic analysis methods are both very important for phylogenomics inference. Based on PCR amplification, a total of 122 markers, which were amplified in 19 representative species, were developed for Laurasiatherian phylogenomics. Subsequently, we illustrated the utility of these newly developed markers using a subset of eight markers. We showed that both 'supermatrix' and 'supertree' trees generated similar topology, which accorded with the current understanding of the Laurasiatherian phylogeny in most aspects. Thus, markers developed here would be likely to make a contribution to resolving evolutionary relationships and inferring evolutionary histories of the Laurasiatherian mammals in the future. 相似文献
963.
964.
【目的】考察泸型酒发酵过程中酒醅细菌群落的演替规律,探讨菌群演替与环境因素变化的相关性。【方法】采用高通量测序技术分析泸型酒酒醅细菌群落的演替规律,并运用Mantel test分析不同发酵阶段的细菌群落演替与环境因素变化的相关性。【结果】酒醅发酵过程中有397个属的微生物,其中Lactobacillus、Bacillus、Weissella、Dysgonomonas、Comamonas以及Ruminococcaceae为优势属(相对丰度1.0%)。通过聚类分析可将酒醅发酵过程划分为3个阶段:阶段I (0–5 d),阶段II (6–17 d)和阶段III(18–40d),且3个阶段的酒醅菌群结构差异显著(P0.05)。Metastats分析结果表明,与阶段I相比,阶段II酒醅细菌群落中Lactobacillus和unclassifiedLactobacillaceae相对丰度显著升高(P0.05),而unclassifiedBacillaceae、 Staphylococcus、 Bacillus、 unclassified Enterobacteriaceae、 Lactococcus、Pseudomonas、Thermoactinomyces、Leuconostoc、Staphylococcus相对丰度显著降低(P0.05)。与阶段II相比,阶段III酒醅细菌群落中Lactobacillus相对丰度显著增长(P0.05),Comamonas、Acetobacter、unclassified Bacilli、Clostridium、Bacillus、Ruminococcus、unclassified Porphyromonadaceae和unclassified Streptophyta相对丰度显著下降(P0.05)。结果表明,阶段I的细菌菌群演替与酒醅温度、水分和乙醇浓度变化线性相关(P0.05);阶段II和阶段III的细菌菌群演替与酒醅温度、水分、酸度、乙醇浓度均没有相关性(P0.05)。【结论】泸型酒酒醅中细菌群落在不同发酵阶段结构差异显著,且温度、水分以及乙醇浓度对酒醅发酵前期(0–5 d)细菌群落演替具有重要作用。 相似文献
965.
966.
967.
Jingjing Chen Shun Xu Shuo Chen Zhihong Zong Xiaoxu Han Yang Zhao Hong Shang 《Biochemical and biophysical research communications》2019,508(3):844-849
CircRNAs are reported to be implicated in the development of lung cancer. This study focused on assessing the expression, functions and molecular mechanism of circPUM1 in lung adenocarcinoma. Here, it showed that circPUM1 is significantly upregulated in both lung adenocarcinoma cell lines and tissues. Furthermore, silencing of circPUM1 impaired the proliferation, migration and invasion ability, and increased apoptosis in A549?cells. Nevertheless, overexpression of circPUM1 in SPC-A1 cells has the opposite effect. Silencing of circPUM1 inhibits the tumorigenesis in nude mice. Mechanistically, circPUM1 could sponge miR-326 and promote the expression of its downstream proteins Cyclin D1 and Bcl-2. In summary, this present study revealed that circPUM1 functions as an oncogene to promote the tumorigenesis of lung adenocarcinoma through circPUM1/miR-326/Cyclin D1 and Bcl-2 axis. This indicates that circPUM1 may act as a potential therapeutic target for lung adenocarcinoma. 相似文献
968.
Isolation and characterization of the cDNA for pulmonary surfactant-associated protein-B (SP-B) in the rabbit 总被引:2,自引:0,他引:2
J J Xu C Richardson C Ford T Spencer L J Yao G Mackie G Hammond F Possmayer 《Biochemical and biophysical research communications》1989,160(1):325-332
Pulmonary surfactant contains phospholipids including dipalmitoyl-phosphatidylcholine and three surfactant-associated proteins designated SP-A, SP-B and SP-C. A cDNA for rabbit SP-B has been isolated from a fetal (30 days gestation) rabbit lung cDNA library constructed in lambda gt11. The cDNA and deduced amino acid sequences show strong homology with the cDNAs and predicted 40 kDa proproteins for human and canine SP-B. Strong homology is also observed with the amino acid sequences directly determined for the mature 8 kDa bovine and porcine SP-B isolated from lung lavage. SP-B is remarkable for its high cysteine and proline content and for the hydrophobic nature of the organic solvent-soluble, mature protein. In vitro translation of sense but not antisense RNA transcribed from the cDNA led to the production of 40 kDa and 32 kDa proteins. These proteins were immunoprecipitated by an antibody raised against bovine SP-B. Northern blot analysis revealed the mRNA for rabbit SP-B appears in fetal rabbit lung late in gestation and falls slightly in the neonate. 相似文献
969.
A Sóoki-Tóth G Bánfalvi J Sz?ll?si E Kirsten M Staub F Antoni E Kun 《Experimental cell research》1989,184(1):44-52
Thymic cells were isolated at intervals of between 0 and 144 h from mice that received one intraperitoneal injection of emetine (33 mg/kg), and thymus weight, incorporation of [14C]leucine into proteins and [3H]thymidine into DNA in intact thymic cells, as well as initial rates of protein ADP-ribosylation in permeabilized cells [A. Sóoki-Tóth, F. Asghari, E. Kirsten, and E. Kun (1987) Exp. Cell Res. 170, 93] were simultaneously monitored. The effect of emetine as an inhibitor of protein synthesis [F. Antoni, N. G. Luat, I. Csuka, I. Oláh, A. Sóoki-Tóth, and G. Bánfalvi (1987) Int. J. Immunopharmacol. 9, 333] corresponds to the induction of sequential cellular events, such as cell exit and remigration, by other antimitotic agents [C. Penit and F. Vasseur (1988) J. Immunol. 140, 3315] and produces an activation of proliferation of cells reentering into this organ. Proliferation, as demonstrated by a large increase in DNA synthesis and entrance into S phase, was kinetically related to an apparent increase in poly(ADP-ribose) polymerase activity in thymic cells and a highly significant in vitro ADP-ribosylation of histone H3. Since no DNA fragmentation occurred in thymic cells, as tested by a fluorometric technique [C. Birnboim and J. J. Jevac (1981) Cancer Res. 41, 1889], it is probable that a selective activation of poly(ADP-ribose) polymerase may have been induced in cells that undergo differentiation and proliferation while repopulating the thymus. 相似文献
970.
黑河下游柽柳种群地上生物量及耗水量的空间分布 总被引:3,自引:2,他引:3
以黑河下游柽柳(Tamarixramosissima)种群为研究对象,通过野外观测,建立柽柳地上生物量与简便易测因子间的关系;利用研究区的高分辨率影像(QuickBird)进行决策树分类,提取出柽柳易测因子的空间分布,估算研究区柽柳生物量的空间分布;在此基础上,借助于柽柳的蒸腾系数(300)计算出整个研究区内柽柳的耗水量.结果表明:研究区柽柳地上生物量为69644.7 t,单位面积生物量为0.78 kg.m-2;河岸边柽柳生境适宜,生物量较大;研究区柽柳蒸散的总水量为2.1×107m3,多年平均耗水量的空间分布范围在30~386 mm. 相似文献