全文获取类型
收费全文 | 1208篇 |
免费 | 157篇 |
国内免费 | 678篇 |
出版年
2024年 | 8篇 |
2023年 | 31篇 |
2022年 | 52篇 |
2021年 | 67篇 |
2020年 | 54篇 |
2019年 | 74篇 |
2018年 | 58篇 |
2017年 | 40篇 |
2016年 | 43篇 |
2015年 | 80篇 |
2014年 | 114篇 |
2013年 | 78篇 |
2012年 | 139篇 |
2011年 | 122篇 |
2010年 | 99篇 |
2009年 | 99篇 |
2008年 | 100篇 |
2007年 | 99篇 |
2006年 | 106篇 |
2005年 | 100篇 |
2004年 | 68篇 |
2003年 | 65篇 |
2002年 | 46篇 |
2001年 | 37篇 |
2000年 | 73篇 |
1999年 | 39篇 |
1998年 | 23篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 14篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有2043条查询结果,搜索用时 15 毫秒
1.
2.
下丘脑外侧区注射TRH对大鼠胃酸分泌的影响 总被引:2,自引:2,他引:0
本文采用连续收集胃腔灌流法,观察下丘脑外侧区(LHA)注射促甲状腺激素释放激素(TRH)对大鼠胃酸分泌的影响,并分析TRH在LHA促进胃酸分泌的作用机制。结果表明:(1)LHA注射TRH(1μg)明显地刺激胃酸分泌;(2)预先向LHA注射酚妥拉明(10μg)、美多心安(5μg)及胃泌素抗体1μl(1:640)并不影响TRH的泌酸作用,如预先向LHA注射阿托品(5μg)则可消除TRH的泌酸效应;(3)垂体摘除及肾上腺切除均不影响TRH的泌酸作用;(4)隔下迷走神经切断后,LHA注入TRH的泌酸效应仍然出现,但持续时间显著缩短;腹腔交感神经节摘除后,TRH仍能促进胃酸分泌,但分泌量少而平稳。以上结果提示:LHA是TRH中枢泌酸效应的有关结构之一,其中枢机制是通过胆碱能M受体中介的,腹腔交感神经节和膈下迷走神经是TRH泌酸效应的传出途径。前者引起的泌酸反应出现较早且引起泌酸高峰,但持续时间短;后者则引起低平的持续分泌。 相似文献
3.
Direct solid phase sequencing of genomic and plasmid DNA using magnetic beads as solid support. 总被引:102,自引:18,他引:84
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Approaches to direct solid phase sequencing of genomic and plasmid DNA have been developed using magnetic beads, coated with streptavidin, as solid support. The DNA is immobilized through selective incorporation of biotin into one of the strands. A single stranded template, suitable for sequencing, is obtained through strand-specific elution. Using this concept, in vitro amplified plasmid DNA and chromosomal DNA were sequenced directly from single colonies. The solid phase approach ensures that the amplification and the sequencing reactions can be performed under optimal conditions. The system was found to be suitable for sequencing using both isotope- and fluorescent-labelled primers. 相似文献
4.
中华白蛉的自育性研究 总被引:3,自引:0,他引:3
现场及实验室结果表明,我国黄土高原的大多数中华白蛉(Phlebotomus chinensis)应属自育性品系,它通常在羽化后、吸血前经交配能依靠腹节内脂肪体发育卵泡,一般在产卵后始行吸血。其生理性状是:胃内无血、腹节内有大量块状或条状脂肪体。羽化24小时后,附腺内有暗色颗粒,卵巢内有发育的卵泡。在25℃士1℃下它的生活史分快、慢两型。快型从卵至成虫仅需44—50夭,慢型需要以四龄幼虫滞育,其长短随滞育期而定,最长的滞育期达301天。观察了白蛉幼虫在饥饿状态下对自育性的影响。此外,还比较了吸血白蛉与自育性白蛉的妊卵数。吸血白蛉的妊卵数约较自育性的高出1/5。这种自育性品系的中华白蛉在自然居群约内占92%、主要栖于洞穴内为野栖种类。本文对自育性中华白蛉的生态及其防制策略作了分析和讨论。 相似文献
5.
Spriet L. L.; Soderlund K.; Bergstrom M.; Hultman E. 《Journal of applied physiology》1987,62(2):611-615
The quadriceps femoris muscles of seven men were electrically stimulated under extended anaerobic conditions to quantitate anaerobic energy release and the contribution of the glycolytic system to total ATP production. Muscles were intermittently stimulated 64 times at 20 Hz while leg blood flow was occluded. Each contraction lasted 1.6 s and was followed by 1.6 s of rest. The total contraction time was 102.4 s. Muscle biopsies were taken at rest and following 16, 32, 48, and 64 contractions. The ATP turnover rates during the four 16-contraction periods were 6.12, 2.56, 2.17, and 0.64 mmol X kg dry muscle-1 X s-1 contraction time. Glycolysis provided 58%, phosphocreatine 40% and a decreased ATP store 2% of the consumed energy during the initial 16 contractions. Glycolysis was responsible for 90% of the total ATP production beyond contraction 16. Absolute glycolytic ATP production decreased to 60, 55, and 17% of the amount in the initial 16 contractions during the final three periods, respectively. In conclusion glycolysis produced approximately 195 mmol ATP/kg dry muscle during the initial 48 contractions (76.8 s) and only approximately 15 mmol ATP/kg dry muscle during the final 16 contractions. Equivalent values for total ATP turnover were 278 and 16.5 mmol/kg dry muscle. 相似文献
6.
Regulation of glycogenolysis in human skeletal muscle 总被引:7,自引:0,他引:7
The role of inorganic phosphate on the regulation of glycogenolysis in resting and contracting muscle was studied in human quadriceps muscle. Increased Pi content was achieved by intermittent electrical stimulation of the muscle followed by occlusion of the blood flow. Occlusion resulted in the maintenance of a high Pi content over a 60-s observation period during which the muscle was either at rest or was stimulated electrically. The study was performed with and without infusion of epinephrine (EPI). In the absence of EPI the phosphorylase a fraction was 50% immediately at the end of the initial stimulation period, declining to 22% after 60 s. With EPI corresponding values for phosphorylase a were 91% initially, 56% after 30 s, and 33% after 60 s, respectively. In both cases the Pi content was increased by approximately 35 mmol/kg dry muscle during the stimulation and remained constant during the occlusion. In neither of these situations was significant degradation of glycogen observed during the occlusion. In the study performed with electrical stimulation during the occlusion period, muscle glycogen degradation was observed both with and without EPI. Phosphorylase a fractions and Pi contents in this study were similar to those observed when muscle was rested over the 60-s occlusion period. The paradox of a high Pi content and extensive transformation of phosphorylase to the a form but low glycogenolytic activity points to additional factors in the regulation of glycogen breakdown. 相似文献
7.
中国拟盘多毛孢属真菌的七个新组合 总被引:4,自引:4,他引:0
作者按照Steyaert(1949)和Sutton(1980)的分类观点,对1987—1988年从我国广西、江西、浙江等地采集的Pestalotiopsis属真菌进行了研究,确认了拟盘多毛孢属真菌的7个新组合种,即Pestalotiopsis carveri(Guba)comb nov.,Pestalotiopsis elasticae(Koord.)comb.nov.,Pestalotiopsis langloisii(Guba)comb.nov.,Pestalotiopsis oleandri(Guba)comb.nov.,Pestalotiopsis sinensis(shen)comb.nov.,Pestalotiopsis sydowiana(Bres.)comb.nov.和Pestalotiopsis zahlbruckneriana(Bres.)comb.nov. 相似文献
8.
斜胸叶蝉属一新种(同翅目:叶蝉总科:耳叶蝉科) 总被引:1,自引:0,他引:1
本文记述耳叶蝉科斜胸叶蝉属一新种:黄缘斜胸叶蝉Epiclinata flavomarinata sp.nov.。标本采自我国西藏。文中描述了新种的外部形态及雄性外生殖器构造特征,并与近似种进行比较,附有主要特征图。模式标本保存于中国科学院动物研究所。 相似文献
9.
Brasilicardin A (BraA)是从致病性放线菌巴西诺卡菌(Nocardia brasiliensis) IFM 0406中发现的具有显著免疫抑制作用(IC50=0.057μg/mL)的二萜糖苷类化合物。BraA发挥免疫抑制活性的作用机制与现有临床常用的免疫抑制剂不同,BraA通过抑制氨基酸转运体L系统的转运进而影响T-淋巴细胞对氨基酸的摄入而发挥免疫抑制作用。相比目前已知的免疫抑制剂环孢菌素A、子囊霉素和他克莫司等,BraA在小鼠混合淋巴细胞反应中显示低毒、高效的优势。因此,BraA作为新型的免疫抑制剂,极具开发潜力,已成为全球免疫抑制剂发现新领域。但其结构复杂、合成困难,原菌种产率低且具有致病性,BraA及其类似物的获得已成为此类新型免疫抑制剂研究的瓶颈。本文综述了BraA的分子特征、药理活性、作用机制、目前获得的BraA类似物和衍生化方面的研究进展,以期为BraA及其类似物的高效生产提供参考。 相似文献
10.
Presence of nadph-cytochrome P-450 reductase in rat liver golgi membranes: Evidence obtained by immunoadsorption method 总被引:26,自引:21,他引:5
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Light Golgi fractions (GF(1+2)) prepared from rat liver homogenates by a modification of the Ehrenreich et al. procedure (J. Cell Biol. 59:45) had significant NADPH-cytochrome P(450) reductase (NADPH-cyt c reductase) activity if assayed immediately after their isolation. An antibody raised in rabbits against purified microsomal and Golgi fractions. To find out whether this activity is located in bona fide Golgi elements or in contaminating microsomal vesicles, we used the following 3-step immunoadsorption procedure: (a) antirabbit IgG (raised in goats) was conjugated to small (2-5 μm) polycrylamide (PA) beads; (b) rabbit anti NADPH-cyt c reductase was immunoadsorbed to the antibody-coated beads; and (c) GF(1+2) was reacted with the beads carrying the two successive layers of antibodies. The beads were then recovered by centrifugation, and were washed, fixed, embedded in agarose, and processed for transmission electromicroscopy. Antireductase- coated beads absorbed 60 percent of the NADPH-cyt c reductase (and comparable fractions of NADH-cyt c reductase and glucose-6-phosphatase) but only 20 percent of the galactosyltransferase activity of the input GF(1+2). Differential vesicle counts showed that approximately 72 percent of the immunoadsorbed vesicles were morphologically recognizable Golgi elements (vesicles with very low density lipoprotein [VLDL] clusters or Golgi cisternae); vesicles with single VLDL and smooth surfaced microsome-like vesicles were too few (approximately 25 percent) to account for the activity. It is concluded that NADPH-cytochrome P(450) reductase is a Golgi membrane enzyme of probably uneven distribution among the elements of the Golgi complex. 相似文献