全文获取类型
收费全文 | 22847篇 |
免费 | 2317篇 |
国内免费 | 2475篇 |
出版年
2024年 | 29篇 |
2023年 | 279篇 |
2022年 | 401篇 |
2021年 | 1105篇 |
2020年 | 943篇 |
2019年 | 1047篇 |
2018年 | 1024篇 |
2017年 | 793篇 |
2016年 | 1039篇 |
2015年 | 1526篇 |
2014年 | 1753篇 |
2013年 | 1798篇 |
2012年 | 2222篇 |
2011年 | 1952篇 |
2010年 | 1260篇 |
2009年 | 1104篇 |
2008年 | 1299篇 |
2007年 | 1124篇 |
2006年 | 1057篇 |
2005年 | 825篇 |
2004年 | 753篇 |
2003年 | 702篇 |
2002年 | 623篇 |
2001年 | 439篇 |
2000年 | 334篇 |
1999年 | 340篇 |
1998年 | 229篇 |
1997年 | 195篇 |
1996年 | 176篇 |
1995年 | 174篇 |
1994年 | 164篇 |
1993年 | 112篇 |
1992年 | 127篇 |
1991年 | 115篇 |
1990年 | 80篇 |
1989年 | 84篇 |
1988年 | 55篇 |
1987年 | 48篇 |
1986年 | 44篇 |
1985年 | 40篇 |
1984年 | 28篇 |
1983年 | 25篇 |
1982年 | 24篇 |
1981年 | 23篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 11篇 |
1976年 | 10篇 |
1975年 | 13篇 |
1972年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
应用PCR技术扩增出HBVDNAC基因片段并与pAT153质粒重组,转化到E.coliRRI中,经体内扩增,提纯,用光生物素标记,制备了C基因的重组质粒探针。该探针检测灵敏度在Southern印迹中达1pg,在点印迹中为5pg。用此探针以Southern印迹方式配合PCR技术检测乙肝病人血清中的HBVDNA,在53例PCR产物电泳检测阴性的样品中,Southern杂交又检出18例阳性。 相似文献
112.
PCR法快速检测临床标本中结核杆菌DNA 总被引:2,自引:0,他引:2
应用聚合酶链反应(PCR)快速检测临床标本(脑脊液、胸水、腹水、血、痰液)中的结核杆菌DNA,特异性扩增片段123bp,为结核杆菌的特异性重复序列IS6110部分基因。PCR检测人型结核杆菌的敏感性达10fgDNA。临床标本的PCR检测阳性率(23.3%)明显高于抗酸染色涂片(2.9%)和细菌培养(5.7%)的阳性率(P〈0.05)。通过设立对照系统及对扩增产物酶切分析,表明该法无假阴性结果(特异 相似文献
113.
森林群落的演替过程,是以各优势种群的动态为其表现特征的。本项研究系统地研究了鼎湖山森林植被演替过程各优势种群的动态。本文研究演替顶极建群种椎栗和荷木等阳生性种群的动态,结果表明其生态位宽度在演替过程中由入侵针叶林起逐渐开始增大,至阳生性为优势常绿阔叶树阶段时为最大,此后渐渐下降,但不会下降为零。在其演变过程中,这些阳生性的种群格局由集群分布演变为趋于随机分布;其与早期先锋种马尾松树种的生态位宽度重叠值和种间联结值由高向低转变,而与中生性树种却有较高的生态位重叠值和种间联结值,但这两方面的值在后期有减弱的趋向。这些结果一方面说明该种群的先锋特性,另一方面也说明由于成熟群落的循环更新使群落结构出现不均匀与镶嵌,使这些阳生性先锋种群 在演替的后期仍以一定数量存在。 相似文献
114.
家鸡和原鸡的线粒体DNA多态性比较 总被引:17,自引:0,他引:17
本文运用11种限制性内切酶分析了家鸡(茶花鸡、尼西鸡、大理漾濞黄鸡)和原鸡共10只个体的线粒体DNA限制性片段长度多态性(RFLP),平均每个个检测到的片段为40条左右。但仅发现3种变异的限制性片制性格局,即StuI-B,Eca-I-b和RI-B.其中StuI-B和ScaI-B为首次报道,而且均为原鸡所物有,EcoRI-B则为大理漾濞黄鸡所特有。茶花鸡和尼西鸡拥有完全相同的限制性格局。经过计算,原 相似文献
115.
笼养白腹锦鸡觅食活动的观察 总被引:10,自引:2,他引:8
笼养条件下白腹锦鸡(Chrysolophus amherstiae)的日觅食活动呈现早(7:00-8:00)和晚(18:00-19:00)两个明显高峰期,不同季节和天气其觅食节律有一定的差异;在一年中9月翌年4月的觅食频次较高,这可能与鸟类补充繁殖期能量消耗、积累能量御寒和保证生殖腺发育有关;逐步回归分析结果表明:影响雄鸟觅食活动的主要因素为求偶、理羽和游走;影响雄鸟觅食的主要因素是游走、理羽和静 相似文献
116.
Nitric oxide and various neuropeptides in the myenteric plexus regulate esophageal motility. We sought colocalization of nitric oxide synthase and neuropeptides in frozen sections of mid-portion of smoothmuscled opossum esophagus using NADPH-diaphorase activity to mark the synthase and immunoreactivity to detect peptides. The peptides, all with demonstrated physiological activity in this organ, were calcitonin generelated peptide, galanin, neuropeptide Y, substance P, and vasoactive intestinal polypeptide. The ExtrAvidin Peroxidase immunostain for each peptide was carried up to the final peroxidase reaction with 3-amino-9-ethylcarbazole. The NADPH-diaphorase reaction was applied with short incubation to provide light staining just before the peroxidase reaction was performed. We examined sections for the proportions of singly and dually labeled nerve cells in the myenteric plexus. NADPH-diaphorase activity was highly colocalized with calcitonin gene-related peptide (59%), galanin (54%), and vasoactive intestinal polypeptide (53%). It showed little colocalization with neuropeptide Y (10%) and substance P (8%). The proportions of all nerve cells containing each of the substances were: NADPH-diaphorase-33%, calcitonin gene-related peptide-30%, galanin-55%, neuropeptide Y-16%, substance P-35%, and vasoactive intestinal polypeptide-58%. We conclude that the nerves responsible for peristalsis in the esophagus may act by releasing nitric oxide along with other inhibitory substances, calcitonin gene-related peptide, galanin, and vasoactive intestinal polypeptide, but not excitatory substances, neuropeptide Y and substance P. 相似文献
117.
Wen Wang Ai-hua Liu Shi-ying Lin Hong Lan Bing Su De-wen Xie Li-ming Shi 《Biochemical genetics》1994,32(9-10):371-378
mtDNA genotypes of six domestic horses (three adult short horses whose heights are under 1 m and three common domestic horses) from a small region of 15 km2 in Malipo county of Yunnan province of China were investigated by the technique of restriction fragment length polymorphism (RFLP) with 16 restriction endonucleases which recognize 6-bp sequences. An average of 56 fragments for an individual was obtained. Unlike other domestic animals, this population of horses exhibits high mtDNA genetic diversity. Each of the six horses has a specific mtDNA genotype showing a pattern of multiple maternal origins, as suggested by fossil and literature records. We think the population of horses is an amazing seed-resource pool of horses and hence deserves to be paid more attention from the view of conservation genetics. However, it is also remarkable that we did not find any typical mtDNA genetic markers which would discriminate between short horses and common domestic horses. 相似文献
118.
Abstract: The Na+ /Ca2+ exchanger is an important element in the maintenance of calcium homeostasis in bovine chromaffin cells. The Na+ /Ca2+ exchanger from other cell types has been extensively studied, but little is known about its regulation in the cell. We have investigated the role of reversible protein phosphorylation in the activity of the Na+ /Ca2+ exchanger of these cells. Cells treated with 1 m M dibutyryl cyclic AMP (dbcAMP), 1 µ M phorbol 12,13-dibutyrate, 1 µ M okadaic acid, or 100 n M calyculin A showed lowered Na+ /Ca2+ exchange activity and prolonged cytosolic Ca2+ transients caused by depolarization. A combination of 10 n M okadaic acid and 1 µ M dbcAMP synergistically inhibited Na+ /Ca2+ exchange activity. Conversely, 50 µ M 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, a protein kinase inhibitor, enhanced Na+ /Ca2+ exchange activity. Moreover, we used cyclic AMP-dependent protein kinase and calcium phospholipid-dependent protein kinase catalytic subunits to phosphorylate isolated membrane vesicles and found that the Na+ /Ca2+ exchange activity was inhibited by this treatment. These results indicate that reversible protein phosphorylation modulates the activity of the Na+ /Ca2+ exchanger and suggest that modulation of the exchanger may play a role in the regulation of secretion. 相似文献
119.
Summary Heavy metals in electroplating effluent inhibited specific methanogenic activity (SMA) of anaerobic starch-degrading granules. The SMA of granules on the degradation of starch were reduced by 50% when each gram of biomass was in contact individually with 105 mg of zinc, 120 mg of nickel, 180 mg of copper, 310 mg of chromium, or >400 mg of cadmium. Granules had higher toxicity-resistance than flocculent sludge, due to their layered structure. 相似文献
120.
Gang Fang K. Venkateswarlu Diane E. Kelly Steven L. Kelly 《Biotechnology letters》1994,16(12):1253-1258
The Saccharomyces cerevisiae strain AH22 was capable of human P4501A1 expression without detectable background of yeast P450, unlike ATCC44773. Repeated backcrossing to AH22 produced a strain allowing transformation by vectors carrying various common selectable markers. Background yeast xenobiotic metabolism was observed only with growth on complex medium. 相似文献