全文获取类型
收费全文 | 10472篇 |
免费 | 1070篇 |
国内免费 | 1692篇 |
出版年
2024年 | 38篇 |
2023年 | 134篇 |
2022年 | 259篇 |
2021年 | 473篇 |
2020年 | 373篇 |
2019年 | 406篇 |
2018年 | 406篇 |
2017年 | 341篇 |
2016年 | 450篇 |
2015年 | 666篇 |
2014年 | 805篇 |
2013年 | 830篇 |
2012年 | 986篇 |
2011年 | 1005篇 |
2010年 | 647篇 |
2009年 | 579篇 |
2008年 | 726篇 |
2007年 | 680篇 |
2006年 | 566篇 |
2005年 | 523篇 |
2004年 | 477篇 |
2003年 | 375篇 |
2002年 | 375篇 |
2001年 | 236篇 |
2000年 | 202篇 |
1999年 | 157篇 |
1998年 | 100篇 |
1997年 | 73篇 |
1996年 | 51篇 |
1995年 | 41篇 |
1994年 | 33篇 |
1993年 | 20篇 |
1992年 | 26篇 |
1991年 | 25篇 |
1990年 | 18篇 |
1989年 | 20篇 |
1988年 | 22篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1974年 | 2篇 |
1965年 | 5篇 |
1961年 | 2篇 |
1955年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
1.
环氧基是一个非常活跃的基团,它能与酶、蛋白质和核酸等生物分子发生反应形成共价键,有利于生物分子的固定化。经共价结合法固定化的酶其稳定性及重复使用性可得到显著提高。用环氧树脂ES-103B为载体采用共价结合法对海洋细菌Bacillus sp. DL-2的胞外蛋白酶进行固定化,经过单因素实验优化条件得出最优固定化条件为:p H 8. 0的胞外蛋白酶溶液,25 g/L的ES-103B,45℃下反应8h。采用此最优条件下的固定化酶拆分(±)-乙酸苏合香酯制备出了e. e. p=97. 5%的(R)-1-苯乙醇(产率为45. 0%)和e. e. s=99. 2%的(S)-乙酸苏合香酯(产率为83. 9%)。该固定化酶拆分(±)-乙酸苏合香酯在重复使用8次后制备出的(R)-1-苯乙醇的e. e. p仍大于90%,且固定化胞外蛋白酶在4℃下具有较好的储存稳定性。 相似文献
2.
Transcriptional regulatory network triggered by oxidative signals configures the early response mechanisms of japonica rice to chilling stress 总被引:3,自引:0,他引:3
3.
4.
格网尺度下典型旅游城市生态服务价值估算和时空分异特征——以三亚为例 总被引:2,自引:0,他引:2
以典型旅游城市三亚市为案例地,利用2006-2018年4期Landsat遥感影像数据,借助ENVI、ArcGIS平台定量识别土地利用演变特征,在1km×1km格网尺度下估算旅游地生态系统服务价值,并结合空间探索性数据分析揭示生态系统服务价值时空分异特征及其与旅游地发展的时空耦合关系。结果表明:(1)2006-2018年间,三亚市生态系统服务价值总量呈逐年下降趋势,由6.73×109元降至5.76×109元,累计减少9.78×108元;(2)空间格局上,三亚市呈"南低北高"空间分异格局,2006-2018年增值区域连片分布于崖州区、天涯区、吉阳区南部区域,且呈逐年减少趋势,减值区域集聚于天涯区东北部、海棠区;(3)空间集聚上,生态系统服务价值截面各年份均呈显著空间正相关且相关性先降后增。高高集聚区位于天涯区北部区域,低低集聚区分布于沿海、海湾地区;(4)旅游发展与生态系统服务价值时空演化特征关联性较强。三亚市天涯区北部林地生态环境良好,生态系统服务价值略有下降但绝对数值稳定,是生态系统服务价值主要来源;旅游发展较为迅速的三亚湾、崖州湾以及海棠湾,相对增值区域较多,但绝对生态系统服务价值损失显著,严重滞后于其他区域。 相似文献
5.
6.
Joohon Sung Kayoung Lee Yun‐Mi Song Mi Kyeong Lee Dong‐Hun Lee 《Obesity (Silver Spring, Md.)》2010,18(5):1000-1005
The heritability of eating behavior and body weight–related traits in Asian populations has not been reported. The purpose of this study was to estimate the heritability of eating behavior and the body weight–related traits of current weight and self‐reported past weight among twins and their families. Study subjects were 2,144 Korean, adult, same‐sex twins and their families at the ages between 20 and 65 years (443 monozygotic (MZ) and 124 dizygotic (DZ) twin pairs, and 1,010 individuals of their family). The Dutch Eating Behavior Questionnaire (DEBQ) was used to assess three eating behavior subscales measuring restraint, emotional eating, and external eating. A variance component approach was used to estimate heritability. After consideration of shared environmental effects and adjustment for age and sex effects, the heritability estimates ± s.e. among twins and their family members were 0.31 ± 0.036 for restraint, 0.25 ± 0.098 for emotional eating, 0.25 ± 0.060 for external eating, 0.77 ± 0.032 for measured current body weight, and 0.70 ± 0.051 for self‐reported weight at 20 years old. The three DEBQ subscales were associated with all weight related traits after adjustment for age and sex. These results suggest eating behaviors and weight‐related traits have a genetic influence, and eating behaviors are associated with obesity indexes. Our findings from Korean twin family were similar to those reported in Western populations. 相似文献
7.
贝壳历来是生物工程和材料学研究的重要对象。贝壳中的贝壳基质蛋白质在贝壳的形成与发育过程中具有重要的调控作用。Whirlin类蛋白质(Whirlin-like protein,WLP)是一种从厚壳贻贝(Mytilus coruscus)中鉴定的新型贝壳基质蛋白质。序列分析结果显示,该蛋白质含有PDZ(postsynaptic density/Discs large/Zonula occludens)结构域,而该结构域对贝壳生物矿化的影响目前尚无报道。为深入了解WLP在贝壳形成中对碳酸钙晶体的影响,在序列分析基础上,采用密码子优化结合原核重组表达,获得其重组表达产物后,开展了重组WLP对碳酸钙晶体形貌及晶型的影响研究,结晶速度抑制以及碳酸钙晶体结合分析。分析结果表明,重组WLP能诱导文石型碳酸钙晶体的形貌和方解石型碳酸钙晶体的晶型发生改变;同时重组WLP对碳酸钙晶体具有结合作用,且能抑制碳酸钙晶体的结晶速度。上述结果表明,WLP对贝壳的形成及发育具有重要影响,并可能在贝壳肌棱柱层的形成中发挥了重要作用。 相似文献
8.
Xu Liu Ben Chen Lulan Chen Wan-Ting Ren Juan Liu Guoxiang Wang Wei Fan Xin Wang Yun Wang 《PloS one》2013,8(4)
Phenol red is widely used in cell culture as a pH indicator. Recently, it also has been reported to have estrogen-like bioactivity and be capable of promoting cell proliferation in different cell lines. However, the effect of phenol red on primary neuronal culture has never been investigated. By using patch clamp technique, we demonstrated that hippocampal pyramidal neurons cultured in neurobasal medium containing no phenol red had large depolarization-associated epileptiform bursting activities, which were rarely seen in neurons cultured in phenol red-containing medium. Further experiment data indicate that the suppressive effect of the phenol red on the abnormal epileptiform burst neuronal activities was U-shape dose related, with the most effective concentration at 28 µM. In addition, this concentration related inhibitory effect of phenol red on the epileptiform neuronal discharges was mimicked by 17-β-estradiol, an estrogen receptor agonist, and inhibited by ICI-182,780, an estrogen receptor antagonist. Our results suggest that estrogen receptor activation by phenol red in the culture medium prevents formation of abnormal, epileptiform burst activity. These studies highlight the importance of phenol red as estrogen receptor stimulator and cautions of careful use of phenol red in cell culture media. 相似文献
9.
Zhaohua Zhang LiLi Ge Shanshan Zhang Jue Wang Wen Jiang Qian Xin Yun Luan 《Journal of cellular and molecular medicine》2020,24(23):13938
The aim of the study was to explore the mechanism of mesenchymal stem cell‐derived exosomes (MSC‐EXO) to protect against experimentally induced pulmonary hypertension (PH). Monocrotaline (MCT)‐induced rat model of PH was successfully established by a single intraperitoneal injection of 50 mg/kg MCT, 3 weeks later the animals were treated with MSC‐EXO via tail vein injection. Post‐operation, our results showed that MSC‐EXO could significantly reduce right ventricular systolic pressure (RVSP) and the right ventricular hypertrophy index, attenuate pulmonary vascular remodelling and lung fibrosis in vivo. In vitro experiment, the hypoxia models of pulmonary artery endothelial cell (PAEC) and pulmonary vascular smooth muscle cell (PASMC) were used. We found that the expression levels of Wnt5a, Wnt11, BMPR2, BMP4 and BMP9 were increased, but β‐catenin, cyclin D1 and TGF‐β1 were decreased in MSC‐EXO group as compared with MCT or hypoxia group in vivo or vitro. However, these increased could be blocked when cells were transfected with Wnt5a siRNA in vitro. Taken together, these results suggested that the mechanism of MSC‐EXO to prevent PH vascular remodelling may be via regulation of Wnt5a/BMP signalling pathway. 相似文献
10.