全文获取类型
收费全文 | 626篇 |
免费 | 76篇 |
国内免费 | 324篇 |
出版年
2024年 | 12篇 |
2023年 | 20篇 |
2022年 | 35篇 |
2021年 | 41篇 |
2020年 | 35篇 |
2019年 | 33篇 |
2018年 | 16篇 |
2017年 | 21篇 |
2016年 | 23篇 |
2015年 | 43篇 |
2014年 | 51篇 |
2013年 | 43篇 |
2012年 | 41篇 |
2011年 | 51篇 |
2010年 | 40篇 |
2009年 | 59篇 |
2008年 | 53篇 |
2007年 | 53篇 |
2006年 | 42篇 |
2005年 | 44篇 |
2004年 | 45篇 |
2003年 | 27篇 |
2002年 | 32篇 |
2001年 | 24篇 |
2000年 | 20篇 |
1999年 | 14篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1975年 | 5篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1967年 | 2篇 |
1962年 | 2篇 |
1950年 | 1篇 |
排序方式: 共有1026条查询结果,搜索用时 15 毫秒
1.
人体单臂间歇运动对发汗调定点的影响 总被引:2,自引:0,他引:2
本工作系在微小气候相对恒定条件下,对10名健康男青年每人进行四项实验。实验 Ⅰ 为测定双侧腿足浸入43℃水中,诱发左前臂屈侧显现定量汗点时的口腔温度(舌下)阈值,作为发汗调定点参考值(ToSSP);实验 Ⅱ 为 Ⅰ 附加右臂间歇轻负荷运动(77W)时测定 ToSSP,部分对象还记录了皮肤电反应;实验 Ⅲ、Ⅳ 为 Ⅰ、Ⅱ 均附加4.5m/s 气流(22—25℃)直吹头面部,再分别测定 ToSSP。实验 Ⅰ 与 Ⅱ 同体对照22人次,Ⅲ 与 Ⅳ 同体对照24人次。结果表明,实验 Ⅱ、Ⅳ 的 ToSSP 均值及其潜伏期均值分别较 Ⅰ、Ⅲ 者降低(P<0.01)或缩短(P<0.001);Ⅰ、Ⅱ间的 ToSSP 均值差、潜伏期均值差,分别与 Ⅲ、Ⅳ 之间者无显著差异(P>0.2);Ⅱ、Ⅳ 的ToSSP 均值各与其实验开始前的口温均值亦无明显差异(P>0.5)。此结果支持运动时体温调定点下降的论点,并提示在研究体温调定点活动时,以 ToSSP 为指标较用发汗速率为优越,因 ToSSP 不为许多干扰因素所影响。 相似文献
2.
The GT2P isoform of microsomal UDP-glucuronosyltransferase from pig liver is a lipid-dependent enzyme. The data in the present work indicate that, in addition to regulation of activity, the thermal stability of the enzyme also is modulated by the acyl chain composition of phosphatidylcholines (PC) used to reconstitute the activity of pure enzyme. There was a reversible, temperature-dependent change in the state of the pure enzyme to an inactive form with onset at T greater than 38 degrees C, depending on the environment of the enzyme. The midpoint for the transition shifted from 39.8 degrees C for enzyme in a bilayer of distearoylphosphatidylcholine (DSPC) to 47.5 degrees C for enzyme in a bilayer of 1-stearoyl-2-oleoylphosphatidylcholine (SOPC). For all lipids, the transition from a catalytically active to an inactive form of the enzyme was associated with large compensating changes in H and S. Lipid-induced stabilization of the active form of UDP-glucuronosyltransferase at T greater than 37 degrees C was associated with decreases in delta H and delta S, but the decreases in delta S were larger, indicating that lipid-induced stabilization of the active form of the enzyme was entropic. The transition between the active and inactive forms of the enzyme was too rapid in either direction to measure in a standard spectrophotometer. In addition to reversible inactivation of the enzyme, there was a slower irreversible, temperature-dependent inactivation. The rate of this process depended on the acyl chains of the phosphocholines interacting with the enzyme. However, there was no obvious correlation between the structures of lipids that stabilized the different inactivation reactions. 相似文献
3.
Transport theory for growing cell populations 总被引:4,自引:0,他引:4
M Rotenberg 《Journal of theoretical biology》1983,103(2):181-199
The partial differential equation that describes the growth of cell populations whose maturation rate is random is developed. The equation resembles that used in classical transport theory but mitotic boundary conditions and the restriction of the maturation rate to non-negative values brings out new features and new problems. This is a generalization of a previously published formulation in which cells could make transitions at random between only two maturation velocities: a characteristic velocity and zero. Growth rates, cycle time distributions and pulsed labeled mitotic curves are calculated for a simple choice of parameters. A numerical algorithm that is suited to the solution of the transport equation is given. 相似文献
4.
5.
从假菠萝麻叶汁中用乙醇分部沉淀法得到一种蛋白酶,对酪蛋白有强烈的水解活性,经Sephadex G-100柱层析和SP-Sephadex C-50离子交换柱层析等步骤纯化,可得到六角形结晶。结晶酶液经PAGE圆盘电泳,每条胶柱上只显示一条蛋白带,其活性在pH4。5-10、55℃范围内较稳定,最适pH8.5最适温度50℃,Km(酪蛋白)值为0.185%(W/V)。用SDS-PAGE和Sephadex 相似文献
6.
本研究旨在建立一种简便、快捷、可直观检测小反刍兽疫病毒(peste des petits ruminants virus,PPRV)抗体的检测方法。将pET-32a-N重组质粒转化至大肠杆菌(Escherichia coli) Rosetta(DE3)感受态细胞中进行诱导表达,以纯化的PPRVN蛋白免疫8周龄BALB/c小鼠,取其脾细胞与SP2/0骨髓瘤细胞进行融合,间接酶联免疫吸附试验(enzyme-linked immunosorbent assays, ELISA)筛选及亚克隆,获得了抗PPRV N蛋白的单克隆抗体。将PPRV N蛋白分别作为金标抗原及检测线(T线)包被抗原、单克隆抗体作为质控线(C线)包被抗体,组装成检测PPRVN蛋白抗体的胶体金免疫层析试纸条。结果显示:成功获得1株能稳定分泌抗N蛋白抗体的杂交瘤细胞株,命名为1F1;间接ELISA检测1F1腹水效价为1:128000;亚类鉴定结果为IgG1,轻链为kappa链。Westernblotting结果显示,1F1能与PPRV N蛋白特异性结合;间接免疫荧光(indirect immunofluorescent ass... 相似文献
7.
目的 鼻咽癌是一种来源于鼻咽上皮的恶性肿瘤,其临床特征之一是易发生淋巴转移,但是目前鼻咽癌转移的分子机制尚未阐明。circPVT1是由PVT1基因2号外显子反向拼接形成的环状RNA (circRNA),在多种肿瘤中表达上调,本文探讨了circPVT1在鼻咽癌侵袭迁移中的作用和分子机制。方法 通过RT-qPCR检测circPVT1及其下游miRNA和FSCN1在鼻咽癌细胞的表达情况,Transwell和划痕愈合实验检测circPVT1对鼻咽癌细胞侵袭迁移的影响,RNA pull-down实验检测circPVT1结合的miRNA,双荧光素酶报告实验检测miR-24-3p和let-7a-5p靶向抑制FSCN1 mRNA表达。结果 在鼻咽癌细胞中过表达circPVT1可以促进鼻咽癌细胞侵袭迁移,而敲低circPVT1则可以抑制鼻咽癌细胞的侵袭迁移。进一步研究发现,circPVT1可以通过竞争性吸附miR-24-3p和let-7a-5p,上调FSCN1的表达,从而促进鼻咽癌细胞的侵袭迁移。结论 circPVT1通过miR-24-3p/let-7a-5p/FSCN1轴促进鼻咽癌细胞侵袭迁移,证实c... 相似文献
8.
A B Vedeniapin V S Rotenberg 《Zhurnal vysshe? nervno? deiatelnosti imeni I P Pavlova》1984,34(2):207-211
Amplitude and latency of skin galvanic response ( SGR ) was studied in 15 healthy subjects in two experimental programs. The first program demanded to perform a motor act as quickly as possible if all the three signals were the same, the second one demanded a motor act if at least one of the signals differed from the other two. Following series of signals were presented: 1--all the three signals being the same, 2--the first one differed from the others, 3,4--correspondingly, the second or the third signal differed from the others. The amplitude of SGR was found to increase, and its latency was found to decrease when the decision was taken under the conditions of time deficit. Thus, SGR reflects the process of decision taking rather than pretuning of the motor act. 相似文献
9.
S B Scholnick P A Caruso J Klemencic G S Mastick C Mauro M Rotenberg 《Developmental biology》1991,146(2):423-437
10.
Isolation, characterization, and expression in Escherichia coli of a cDNA encoding rat heme oxygenase-2 总被引:15,自引:0,他引:15
In a recent study (Cruse, I., and Maines, M.D. (1988) J. Biol. Chem. 263, 3348-3353), we reported the isolation of a small cDNA fragment encoding a portion of heme oxygenase-2 through immunological screening of a rat testis cDNA library in lambda gt11. We have now used this 274-base pair (bp) cDNA fragment as a hybridization probe for rescreening of the same library, and have thereby recovered a number of additional positive isolates. Of these, three candidates of approximately 900, 1100, and 1300 bp, respectively, were subsequently subcloned and sequenced. Although differing in length, the sequences of these clones were found to be otherwise identical. Moreover, the length of isolate 18B, 1284 bp, corresponded well with that of the single mRNA species (approximately 1300-1350 nucleotides) detected through Northern blot hybridization analysis of rat testis total and poly(A)+RNA. This full- or near full-length cDNA encodes a 315-amino acid protein with a molecular weight of 35,757, in good agreement with the 36,000 estimated molecular weight of heme oxygenase-2. When expressed in Escherichia coli, cDNA encodes a protein that cross-reacts with heme oxygenase-2 antiserum (as assayed by Western immunoblotting) and yields high levels of heme oxygenase activity in bacterial soluble cell extracts. Finally, computer analysis of the heme oxygenase-2 cDNA sequence indicates that the predicted amino acid sequence and hydropathy profile of the heme oxygenase-2 protein exhibit similarity with heme oxygenase-1. 相似文献