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   8313篇
  免费   208篇
  国内免费   5篇
电工技术   54篇
综合类   4篇
化学工业   964篇
金属工艺   76篇
机械仪表   101篇
建筑科学   162篇
矿业工程   27篇
能源动力   106篇
轻工业   360篇
水利工程   65篇
石油天然气   10篇
无线电   263篇
一般工业技术   875篇
冶金工业   4875篇
原子能技术   34篇
自动化技术   550篇
  2023年   25篇
  2022年   44篇
  2021年   79篇
  2020年   59篇
  2019年   90篇
  2018年   84篇
  2017年   78篇
  2016年   107篇
  2015年   79篇
  2014年   110篇
  2013年   264篇
  2012年   210篇
  2011年   297篇
  2010年   224篇
  2009年   197篇
  2008年   260篇
  2007年   246篇
  2006年   212篇
  2005年   180篇
  2004年   147篇
  2003年   133篇
  2002年   119篇
  2001年   92篇
  2000年   80篇
  1999年   177篇
  1998年   1246篇
  1997年   780篇
  1996年   525篇
  1995年   293篇
  1994年   281篇
  1993年   278篇
  1992年   94篇
  1991年   70篇
  1990年   91篇
  1989年   94篇
  1988年   75篇
  1987年   84篇
  1986年   81篇
  1985年   64篇
  1984年   45篇
  1983年   50篇
  1982年   57篇
  1981年   59篇
  1980年   81篇
  1979年   21篇
  1978年   30篇
  1977年   127篇
  1976年   281篇
  1975年   22篇
  1973年   17篇
排序方式: 共有8526条查询结果,搜索用时 31 毫秒
991.
OBJECTIVE: In women who use oral contraceptives with low estrogen doses, a quiescent endometrium is frequently produced. Further reduction of the estrogen dose would not be expected to alter this effect. In this open-label study, the effects on the endometrium of a monophasic oral contraceptive containing 75 micrograms gestodene and 20 micrograms ethinylestradiol were assessed. METHOD: Biopsies were performed on 25 women on therapy. The biopsies were performed during the late luteal phase (last 7 days) in the pretreatment cycle and during days 15-21 in cycle 6 for 13 subjects (Group A) and during days 15-21 in cycle 3 and during the late luteal phase (last 7 days) in the post-treatment cycle for 12 subjects (Group B). RESULTS: All subjects completed six cycles of treatment. Nine of 13 subjects pretreatment and nine of 12 subjects at cycle 3 were characterized by the pathologist as having a secretory endometrium. Four of 13 subjects at cycle 6 and ten of 11 subjects post-treatment also demonstrated a secretory endometrium. Pre-decidual changes were seen in one, two, two and zero subjects at pretreatment, after three cycles, six cycles, and post-treatment, respectively. Six subjects had an atrophic endometrium at cycle 6. CONCLUSIONS: With monophasic gestodene/ethinylestradiol 75 micrograms/20 micrograms, a secretory or inactive endometrium was present in most subjects. Thus, the effects on the endometrium of this oral contraceptive containing a reduced estrogen dose are consistent with those produced by other low-estrogen-dose combination oral contraceptives.  相似文献   
992.
We present here some sensitive optical and mechanical experiments for monitoring the process of formation and growth of two-dimensional (2D) crystals of proteins on a lipid monolayer at an air-water interface. The adsorption of proteins on the lipid monolayer was monitored by ellipsometry measurements. An instrument was developed to measure the shear elastic constant (in plane rigidity) of the monolayer. These experiments have been done using cholera toxin B subunit (CTB) and annexin V as model proteins interacting with a monosialoganglioside (GM1) and dioleoylphosphatidylserine (DOPS), respectively. Electron microscopy observations of the protein-lipid layer transferred to grids were systematically used as a control. We found a good correlation between the measured in-plane rigidity of the monolayer and the presence of large crystalline domains observed by electron microscopy grids. Our interpretation of these data is that the crystallization process of proteins on a lipid monolayer passes through at least three successive stages: 1) molecular recognition between protein and lipid-ligand, i.e., adsorption of the protein on the lipid layer; 2) nucleation and growth of crystalline patches whose percolation is detected by the appearance of a non-zero in-plane rigidity; and 3) annealing of the layer producing a slower increase of the lateral or in-plane rigidity.  相似文献   
993.
The National Practitioner Data Bank (NPDB), created by the 1986 Health Care Quality Improvement Act, has been in operation since 1990. Hospitals and other credentialing bodies must query the NPDB when granting and renewing privileges. The NPDB receives about 25,000 reports of adverse actions against health practitioners each year. The NPDB was designed to be a flagging system providing information to licensing or credentialing authorities who would further examine practitioner records. Its purpose is to ensure that decision makers have information that might not otherwise be readily available, especially in the case of incompetent practitioners who move from hospital to hospital or state to state. Access to NPDB information is a concern for consumers and providers alike. Only 2% of matched reports to the NPDB made a difference in hospital privileging decisions. A limitation of NPDB information is that malpractice payments recorded in the NPDB do not necessarily constitute a comprehensive and definitive reflection of actual health care incompetence. All health care providers need to be aware of the NPDB, its mission, potential impact on their ability to be credentialed, and proposed additional uses of its information.  相似文献   
994.
995.
To better understand mechanisms that limit rAAV transduction in the lung, we have evaluated several unique features of rAAV infection in polarized primary airway epithelial cultures. rAAV was found to transduce the basolateral surface of airway epithelia 200-fold more efficiently than the apical membrane. These differences in membrane infection correlated with the abundance of apical heparan sulfate proteoglycan (AAV-2 receptor) and virus binding. UV irradiation augmented rAAV transduction greater than 20-fold, only when virus was applied to the apical membrane. Ultrastructural analysis of UV-irradiated primary cultures demonstrated significant changes in microvilli architecture following exposure to 25 J/m2 UV. Although virus binding and the abundance of heparan sulfate proteoglycan were not increased at the apical membrane following UV irradiation, increased receptor-independent endocytosis of fluorescent beads was seen at the apical membrane following UV irradiation. We hypothesize that endocytotic processes associated with apical membrane-specific pathways of viral entry, and/or processing of virus to the nucleus, may be altered following UV irradiation. Interestingly, UV irradiation had an inhibitory effect on rAAV transduction from the basolateral membrane, which correlated with a decrease in the abundance of heparan sulfate proteoglycan at the basal membrane. In summary, these findings suggest that independent pathways of viral transduction may occur in the apical and basolateral compartments of polarized airway epithelia.  相似文献   
996.
Budding yeast replication origins are activated during S phase according to a predetermined temporal programme. Two recent studies indicate that this programme is executed, at least in part, by the S-phase-promoting cyclins that act to assemble a pre-initiation complex which includes the Cdc45 protein.  相似文献   
997.
Four studies bridged the areas of personality–mood and mood–cognition relations by investigating the effects of Extraversion and Neuroticism on the evaluation of affectively pleasant, unpleasant, and neutral word pairs. Specifically measured were affectivity ratings, categorization according to affect, judgments of associative strength, and response latencies. A strong, consistent cognitive bias toward affective as opposed to neutral stimuli was found across participants. Although some biases were systematically related to personality and mood, effects of individual differences were present only under specific conditions. The results are discussed in terms of a personality–mood framework and its implications for cognitive functioning. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
998.
999.
We examined the effects from subjects, technicians and spirometers on within-session variability in successful recordings of forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) in 4989 asymptomatic never-smoking men. All eligible men aged 30-46 years living in western Norway (n = 45,380) were invited to a cross-sectional community survey. Information on respiratory symptoms, smoking habits and occupational exposures was obtained from a self-administered questionnaire. Three successful FEV1 and FVC recordings were obtained in 26,368 attendants using three dry-wedge bellow spirometers operated by 10 different technicians. Within-subject standard deviation (SD) from three recordings of FEV1 and FVC was on average 102 and 106 ml, respectively, and increased with height (14 and 17 ml, respectively, per 10 cm) and body mass index (BMI) (11 and 14 ml, respectively, per 5 kg m-2). Between-subject SD of the mean of three FEV1 and FVC recordings was 591 and 754 ml, respectively, and increased in groups of increasing height (43 and 40 ml, respectively, per 10 cm). Small, but significant, differences were observed between technicians in within-subject SD and in levels of FEV1 and FVC. Homogeneity of between-subject variability, necessary for linear regression analysis, was obtained using FEV1 and FVC divided by height squared. In conclusion, within-subject variability in three successful spirometric recordings was small, but dependent on height and BMI of the subjects as well as technician performance. The observed heterogeneity in between-subject variation in FEV1 and FVC levels disappeared when each variable was divided by height squared. Novel multiple linear regression equations for FEV1/height2 and FVC/height2 were developed to be used in evaluating the effects from occupational airborne exposures in Nordic men aged 30-46 years.  相似文献   
1000.
The present research addresses whether rats can express odor aversions to the odor of taste stimuli. In Experiment 1, saccharin or salt were either mixed in distilled water, so the rats could taste and smell them, or presented on disks attached to the tubes' metal spouts so the rats could only smell them. Aversions were established to taste stimuli under both conditions. The results of Experiment 2 indicate that conditioning was to the odor of the tastes when they were presented on disks in Experiment 1, hence both taste and odor aversions were established by means of "taste" stimuli. Taste aversion learning thus may more properly be termed flavor aversion learning, with flavor referring to both taste and odor components. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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