全文获取类型
收费全文 | 8309篇 |
免费 | 172篇 |
国内免费 | 73篇 |
专业分类
电工技术 | 69篇 |
综合类 | 57篇 |
化学工业 | 622篇 |
金属工艺 | 77篇 |
机械仪表 | 97篇 |
建筑科学 | 188篇 |
矿业工程 | 35篇 |
能源动力 | 64篇 |
轻工业 | 423篇 |
水利工程 | 41篇 |
石油天然气 | 56篇 |
武器工业 | 6篇 |
无线电 | 309篇 |
一般工业技术 | 650篇 |
冶金工业 | 5386篇 |
原子能技术 | 35篇 |
自动化技术 | 439篇 |
出版年
2022年 | 30篇 |
2021年 | 65篇 |
2020年 | 39篇 |
2019年 | 33篇 |
2018年 | 74篇 |
2017年 | 51篇 |
2016年 | 71篇 |
2015年 | 67篇 |
2014年 | 79篇 |
2013年 | 228篇 |
2012年 | 144篇 |
2011年 | 191篇 |
2010年 | 150篇 |
2009年 | 157篇 |
2008年 | 192篇 |
2007年 | 188篇 |
2006年 | 154篇 |
2005年 | 152篇 |
2004年 | 103篇 |
2003年 | 120篇 |
2002年 | 96篇 |
2001年 | 83篇 |
2000年 | 95篇 |
1999年 | 224篇 |
1998年 | 1598篇 |
1997年 | 882篇 |
1996年 | 576篇 |
1995年 | 331篇 |
1994年 | 293篇 |
1993年 | 335篇 |
1992年 | 75篇 |
1991年 | 79篇 |
1990年 | 114篇 |
1989年 | 96篇 |
1988年 | 88篇 |
1987年 | 112篇 |
1986年 | 85篇 |
1985年 | 110篇 |
1984年 | 56篇 |
1983年 | 44篇 |
1982年 | 50篇 |
1981年 | 56篇 |
1980年 | 64篇 |
1979年 | 28篇 |
1978年 | 48篇 |
1977年 | 143篇 |
1976年 | 267篇 |
1975年 | 32篇 |
1974年 | 23篇 |
1973年 | 20篇 |
排序方式: 共有8554条查询结果,搜索用时 15 毫秒
1.
2.
Apolipoprotein E plays a central role in clearance of lipoprotein remnants by serving as a ligand for low-density lipoprotein and apolipoprotein E receptors. Three common alleles (apolipoprotein E(2), E(3) and E(4)) give rise to six phenotypes. Apolipoprotein E(3) is the ancestral form. Common apolipoprotein E isoforms derive from nucleotide substitutions in codons 112 and 158. Resulting cysteine-arginine substitutions cause differences in: affinities for low-density lipoprotein and apolipoprotein E receptors, low-density lipoprotein receptor activities, distribution of apolipoprotein E among lipoproteins, low-density lipoprotein formation rate, and cholesterol absorption. Accompanying changes in triglycerides, cholesterol and low-density lipoprotein may promote atherosclerosis development. Over 90% of patients with familial dysbetalipoproteinaemia have apolipoprotein E(2)/E(2). Apolipoprotein E(4) may promote atherosclerosis by its low-density lipoprotein raising effect. Establishment of apolipoprotein E isoforms may be important for patients with diabetes mellitus and several non-atherosclerotic diseases. Apolipoprotein E phenotyping exploits differences in isoelectric points. Isoelectric focusing uses gels that contain pH 4-7 ampholytes and urea. Serum is directly applied, or prepurified by delipidation, lipoprotein precipitation or dialysation. Isoelectric focusing is followed by immunofixation/protein staining. Another approach is electro- or diffusion blotting, followed by protein staining or immunological detection with anti-apolipoprotein E antibodies and an enzyme-conjugated second antibody. Apolipoprotein E genotyping demonstrates underlying point mutations. Analyses of polymerase chain reaction products are done by allele-specific oligonucleotide probes, restriction fragment length polymorphism, single-stranded conformational polymorphism, the primer-guided nucleotide incorporation assay, or denaturating gradient gel electrophoresis. Detection with primers that either or not initiate amplification is performed with the amplification refractory mutation system. Disparities between phenotyping and genotyping may derive from isoelectric focusing methods that do not adequately separate apolipoprotein E posttranslational variants, storage artifacts or faint isoelectric focusing bands. 相似文献
3.
Within the realm of oncology nursing, research has been an integral part in its development as a specialty practice. Yet despite the growing volume of published nursing research studies, little is known about how nurses working in oncology care settings perceive research. Therefore, the purposes of this study were to examine clinical oncology nurses' perceptions of research and to determine factors influencing their perceptions. Two hundred and eighty-three registered nurses providing cancer care to patients in 40 health care agencies across northern Ontario participated in the survey. Data were collected using a questionnaire developed by Alcock and colleagues (1990) which addressed nurses' perceived value of research, their role, interest and experience in research as well as the research climate of the agency. The findings showed that respondents valued nursing research and perceived a research role for staff nurses. However, the respondents did not perceive strong administrative or collegial support for nurses' involvement in research activities. In addition, the study results indicated that the clinical oncology nurses' perceptions of research were influenced by educational preparation. 相似文献
4.
Adaptive increases in renal bicarbonate reabsorption occur in response to acute increases in filtered bicarbonate (FLHCO3). In a previous study, we showed that an increase in FLHCO3 induced by plasma volume expansion increased the Vmax for Na+/H+ exchange activity in renal cortical brush border membrane vesicles (BBMV), providing a potential mechanism for the adaptive increase in HCO3- reabsorption. The present studies were undertaken to determine whether the increase in FLHCO3 induced by plasma expansion also stimulates the other major H+ transporter in cortical BBMV, the H(+)-ATPase. H(+)-ATPase activity was assessed in BBMV obtained from hydropenic and plasma expanded Munich-Wistar rats, using a NADH-linked ATPase assay. H(+)-ATPase activity was measured as the ouabain and oligomycin-insensitive, bafilomycin A1-sensitive component of total ATPase activity. Acute plasma expansion doubled single nephron FLHCO3, and this change was associated with a 64% increase in the Vmax for H(+)-ATPase activity, with no change in apparent Km. The Vmax for H(+)-ATPase activity correlated directly with whole kidney GFR and FLHCO3 (r = 0.68 and 0.72, respectively), and with single nephron GFR and FLHCO3 (r = 0.76 and 0.80, respectively). Thus, the mechanism for the adaptive increase in proximal tubular HCO3- reabsorption that occurs in response to acute increases in FLHCO3 appears to be related to increased activity of both H(+)-ATPase and Na+/H+ exchange in the apical membrane of the proximal tubule epithelium. 相似文献
5.
6.
7.
8.
9.
A program called GELYMAC takes data on the distances migrated by DNA fragments in a one-dimensional electrophoretic gel and, using a cubic-spline best-fit of marker fragment distance migrated versus molecular size, calculates the molecular sizes of the fragments. Written in the Rascal (Real-time Pascal) programming language, the program runs on the Macintosh family of microcomputers. Rapid entry of marker and experimental fragment migration data is afforded using a scroll bar system adjacent to a graphic representation of a gel. Output includes tabular listing of the data, graphic cartoons of the gel, and the fragment locations and molecular sizes for individual gel lanes, and the calibration curve used in data computations. 相似文献
10.