首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4039篇
  免费   62篇
  国内免费   9篇
电工技术   18篇
综合类   10篇
化学工业   348篇
金属工艺   101篇
机械仪表   66篇
建筑科学   106篇
矿业工程   12篇
能源动力   52篇
轻工业   194篇
水利工程   20篇
石油天然气   11篇
武器工业   1篇
无线电   144篇
一般工业技术   346篇
冶金工业   2352篇
原子能技术   13篇
自动化技术   316篇
  2022年   15篇
  2021年   14篇
  2019年   12篇
  2018年   25篇
  2017年   24篇
  2016年   30篇
  2015年   33篇
  2014年   38篇
  2013年   99篇
  2012年   68篇
  2011年   89篇
  2010年   67篇
  2009年   61篇
  2008年   68篇
  2007年   85篇
  2006年   83篇
  2005年   96篇
  2004年   67篇
  2003年   73篇
  2002年   80篇
  2001年   51篇
  2000年   49篇
  1999年   109篇
  1998年   631篇
  1997年   392篇
  1996年   258篇
  1995年   152篇
  1994年   144篇
  1993年   159篇
  1992年   39篇
  1991年   40篇
  1990年   49篇
  1989年   52篇
  1988年   60篇
  1987年   58篇
  1986年   47篇
  1985年   56篇
  1984年   38篇
  1983年   36篇
  1982年   39篇
  1981年   42篇
  1980年   35篇
  1979年   23篇
  1978年   31篇
  1977年   63篇
  1976年   144篇
  1975年   30篇
  1974年   18篇
  1973年   20篇
  1972年   19篇
排序方式: 共有4110条查询结果,搜索用时 15 毫秒
51.
Erythropoietin excretion was persistently increased following major thermal injury in 4 of 5 patients. A good correlation was found between erythropoietin excretion and red cell mass but not between erythropoietin excretion and hematocrit. In spite of the increased erythropoietin, erythropoiesis in these thermally injured patients was inadequate to compensate for erythrocyte deficits as judged by bone marrow morphology, reticulocyte counts, and transfusion requirements.  相似文献   
52.
Argues that a number of unsolved issues confront the behavioral sciences in medical education and that the most pressing problem is the type of core basic science curriculum that should be provided. The behavioral sciences often seem to fail in their teaching mission because they do not provide that information which can be "converted" into specific clinical skills. Recent studies of behavioral science programs at 9 major medical schools underscore the fact that there is no unanimity of opinion about the material that should be taught to all medical students. Although diversity is valuable because it promotes experimentation with curricula, the behavioral sciences, particularly psychology, should develop a model of the doctor's job which contains the basic information required for primary patient care. Some examples of clinically applicable behavioral science content that could be included in all curricula are suggested. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
53.
Studied self-monitoring of eyeblink responses in 80 undergraduate volunteers to test hypotheses that (a) the direction of reactive effects is a function of the perceived value of the target behavior; (b) neither the behavior's value nor self-monitoring alone is sufficient to produce significant effects but that both are necessary; (c) self-monitoring is more reactive than monitoring by the E; (d) multiple reports of monitoring are more reactive than a single report of monitoring; and (e) self-monitoring effects are more reactive than a single report of merely attending to a particular behavior. Results provide general support for the 1st 2 hypotheses and suggestive support for the 3rd. Results pertaining to the 4th and 5th hypotheses took an unexpected twist and suggest the need for further study. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
54.
Effect of charcoal-broiled beef on phenacetin metabolism in man   总被引:1,自引:0,他引:1  
When charcoal-broiled beef was fed to human volunteers, who were then given phenacetin orally, the concentration of phenacetin in the plasma was lowered, but its half-life in the plasma was not changed. The data suggest that feeding charcoal-broiled beef enhances the metabolism of orally administered phenacetin in the intestine or during its first pass through the liver, or both.  相似文献   
55.
Clearance curves for arterial and coronary-venous blood were determined after systemic left-ventricle or pulmonary-artery infections of 133Xe, paired with selective left-coronary-artery injections of 133Xe in 20 dogs with closed chest. Coronary blood flows calculated from systemic and coronary-artery injections were comparable only when a correction was made for arteriol recirculation of 133Xe following the systemic injection (r = 0.962) for left ventricle and 0.932 for pulmonary artery, paired with coronary artery). Experiments in four other dogs, verified that clearance of 133Xe from the pulmonary circulation was only about 60%. The myocardium/blood 133Xe partition coefficient, determined in vivo in ten dogs, agreed within 10% with that previously determined in vitro.  相似文献   
56.
Both prepubertal and adult rats were treated with a single oral dose of either 60 mg or 120 mg of dl-6-(N-pipecolinomethyl)-5-hydroxy indane maleate (PMHI) per kg of body weight. Their testicular weights were drastically reduced compared with those of the controls. A follow-up, beginning on the third day post-treatment and continuing for a period of 50 days, showed that the body weight growth of PMHI-treated rats was not retarded. The hormonal profile indicated that, except for FSH which showed a transitory elevation in PMHI-treated immature rats, the serum levels of LH, estrogen, and testosterone were indistinguishable from those of the controls. Testicular histology revealed that the spermatogenic process in PMHI-treated rats recovered at a dose-related rate. EM sections of testes of adult rats indicated that cytoplasmic vacuolation appeared in the Sertoli cells 5 h post-treatment. The consequent cascade of arrested spermiogenesis included abnormal acrosomal condensation of spermatids and sloughing of polynucleated spermatids. Some spermatocytes also seemed to be affected, but spermatogonia and Leydig cells remained intact. These results indicate the PMHI acts primarily on Sertoli cells and causes arrest in the spermiogenetic stage of the spermatids. At a higher and toxic dose of PMHI, however, the earlier germinal elements might also be affected, due to the extensive damage to the supporting Sertoli cells.  相似文献   
57.
Thin polymer films were irradiated in a high vacuum environment with energetic (~2 MeV) ions. The emitted molecular species were studied with a quadrupole mass spectrometer during bombardment. The emitted species are predominantly small molecules. The efficiency of emission depends strongly upon the electronic energy loss of the incident ions in the film and, hence, upon the velocity and atomic number of the incident ion. The emission efficiency of all species decreases with increasing damage in the film. By pulsing the ion beam, the time dependence of irradiation induced emission of molecular species from the films has been studied. Emission delays of hundreds of milliseconds are observed in some cases. These delays are found to depend upon the emitted species as well as the host film and seem to be associated with diffusion of the species in the films.  相似文献   
58.
首先通过体外模拟唾液-胃液-肠液应激实验研究乳杆菌的耐消化应激能力,然后研究其对肠道黏蛋白和Caco-2细胞的黏附及抑制肠道病原菌黏附的能力,最后探讨消化应激对乳杆菌黏附能力的影响。结果表明,副干酪乳杆菌W125、m111和发酵乳杆菌146在依次经过模拟唾液-胃液-肠液应激后存活率分别为2.70%、3.53%及11.15%,活菌数分别为7.46、7.24(lg(CFU/mL))及8.35(lg(CFU/mL)),且对黏蛋白和Caco-2细胞的黏附率显著高于其他菌株(P<0.05),分别为15.67%、8.75%、8.38%和11.47%、21.34%、10.44%;3株菌株均可通过排除、竞争和替代的方式抑制大肠杆菌CICC10899和沙门菌WX29对肠道的黏附,黏附抑制率均大于13.51%;消化应激显著降低了副干酪乳杆菌W125和发酵乳杆菌146对肠道的黏附能力(P<0.05),但显著增加了副干酪乳杆菌m111的黏附能力(P<0.05),黏附率由17.60%增加到30.45%,且主要黏附素由消化应激前的表层蛋白变为应激后的蛋白和多糖;消化应激前后副干酪乳杆菌m111均...  相似文献   
59.
Infertility represents a major clinical problem and 50% of cases are attributable to the male partner. Testicular function is temperature dependent, and in both man and mouse the position of the testes in the scrotum ensures that they are kept at between 2 and 8 degrees C below core body temperature. We used a mouse model to investigate the impact of a single, transient, mild, scrotal heat stress (38, 40 or 42 degrees C for 30 min) on testicular function, sperm DNA integrity and embryo survival. We detected temperature-dependent changes in testicular architecture, number of apoptotic cells and a significant reduction in testis weight 7 and 14 days after heat stress at 42 degrees C. We report for the first time that DNA strand breaks (gamma-H2AX-positive foci) were present in spermatocytes recovered from testes subjected to 40 or 42 degrees C. Fertility of heat-stressed males was tested 23-28 d after treatment (sperm at this time would have been spermatocytes at time of heating). Paternal heat stress at 42 degrees C resulted in reduced pregnancy rate, placental weight and litter size; pregnancies from the 40 degrees C group had increased resorptions at e14.5. Abnormalities in embryonic development were detected at e3.5 and in vitro fertilisation with sperm recovered 16 h or 23 d after scrotal stress at 42 degrees C revealed a block in development between the 4-cell and blastocyst stages. This study has provided evidence of temperature-dependent effects on germ cell DNA integrity and highlighted the importance of an intact paternal genome for normal embryo development.  相似文献   
60.
The current study evaluated exosomes isolated from plasma of heifers bred to have high or low fertility through developing extreme diversity in fertility breeding values, however, key animal traits (e.g., body weight, milk production, and percentage of North American genetics) remained similar between the 2 groups. The exosomes were isolated by a combined ultracentrifugation and size exclusion chromatography approach and characterized by their size distribution (nanoparticle tracking analysis), morphology (transmission electron microscopy), and presence of exosomal markers (immunoblotting). In addition, a targeted mass spectrometry approach was used to confirm the presence of 2 exosomal markers, tumor susceptibility gene 101 and flotillin 1. The number of exosomes from plasma of high fertility heifers was greater compared with low fertility heifers. Interestingly, the exosomal proteomic profile, evaluated using mass spectrometry, identified 89 and 116 proteins in the high and low fertility heifers respectively, of which 4 and 31 were unique, respectively. These include proteins associated with specific biological processes and molecular functions of fertility. Most notably, the tetratricopeptide repeat protein 41-related, glycodelin, and kelch-like protein 8 were identified in plasma exosomes unique to the low fertility heifers. These proteins are suggested to play a role in reproduction; however, the role of these proteins in dairy cow reproduction remains to be elucidated. Their identification underscores the potential for proteins within exosomes to provide information on the fertility status and physiological condition of the cow. This may potentially lead to the development of prognostic tools and interventions to improving dairy cow fertility.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号