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   993篇
  免费   20篇
  国内免费   1篇
电工技术   9篇
综合类   1篇
化学工业   72篇
金属工艺   16篇
机械仪表   14篇
建筑科学   37篇
矿业工程   4篇
能源动力   10篇
轻工业   103篇
水利工程   7篇
石油天然气   11篇
无线电   69篇
一般工业技术   145篇
冶金工业   355篇
原子能技术   7篇
自动化技术   154篇
  2022年   8篇
  2020年   9篇
  2019年   22篇
  2018年   17篇
  2017年   9篇
  2016年   12篇
  2015年   8篇
  2014年   19篇
  2013年   45篇
  2012年   39篇
  2011年   40篇
  2010年   36篇
  2009年   25篇
  2008年   52篇
  2007年   45篇
  2006年   38篇
  2005年   40篇
  2004年   26篇
  2003年   15篇
  2002年   27篇
  2001年   26篇
  2000年   21篇
  1999年   13篇
  1998年   66篇
  1997年   31篇
  1996年   20篇
  1995年   22篇
  1994年   21篇
  1993年   21篇
  1992年   18篇
  1991年   7篇
  1990年   17篇
  1989年   14篇
  1988年   8篇
  1987年   21篇
  1986年   13篇
  1985年   9篇
  1984年   12篇
  1983年   8篇
  1982年   7篇
  1981年   11篇
  1980年   8篇
  1979年   12篇
  1978年   8篇
  1977年   12篇
  1976年   17篇
  1975年   7篇
  1974年   3篇
  1973年   6篇
  1971年   5篇
排序方式: 共有1014条查询结果,搜索用时 15 毫秒
81.
OBJECTIVE: To investigate why women who use crack cocaine are at increased risk of human immunodeficiency virus (HIV) infection. METHODS: One thousand one hundred fifty-two (99.7%) of 1155 consecutive prenatal patients attending a rural public health clinic were interviewed about drug use and sexual practices and tested for HIV infection and other sexually transmitted diseases. RESULTS: Fifty-one (4.7%) of 1096 pregnant women reported ever using crack cocaine, but only five (10%) of the crack cocaine users had ever injected drugs. Eighteen (35%) of the crack users were HIV infected compared with 22 (2%) of the 1045 women who reported never using crack (odds ratio 25, 95% confidence interval 12-52; P < .001). Crack users were more likely to have had a known HIV-infected sex partner, exchanged sex for money or drugs, and tested positive for syphilis than were non-crack users (for each comparison, P < .001). Before using crack, 18% of crack users had exchanged sex for money or drugs and 8% had averaged three or more sex partners per month; in contrast, after beginning to use crack, 76% of crack users exchanged sex for money or drugs and 63% averaged three or more sex partners per month (for both comparisons, P < .001). Crack users who were not HIV infected were more likely to have almost always used condoms and/or had fewer than three sex partners per month than were HIV-infected crack users (P < .01). CONCLUSION: Women who reported using crack cocaine were at an increased risk of HIV infection because crack use was associated with a significant increase in unprotected sexual contact.  相似文献   
82.
83.
Forgiveness is one construct that is beginning to demonstrate promise as a health and relationship promoter within the workplace. The primary aim of this research was to examine the effects of one psychological intervention (social motivational training) that was developed to promote forgiveness among co-workers. In the first of two studies, workers were randomly assigned to one of two intervention conditions (i.e., job satisfaction training, social motivational training). Participants read a vignette in which they were to imagine themselves as victims of a co-worker transgression. Judgments of responsibility and co-worker forgiveness were then measured at two intervals: before and after training. In Study 2, workers recounted an actual critical incident involving a co-worker transgression, completed a pretraining questionnaire measuring judgments of responsibility, self-image, and forgiveness, received either a one-on-one job satisfaction training or social motivational training session, and completed a post-training questionnaire. Results from both studies indicated that social motivational training enhanced participants' forgiveness of a hypothetical and actual co-worker. In addition, Study 2 showed an increase in workers' self-image following social motivational training, suggesting affirmation of the self as a possible mechanism for the effects of social motivational training on forgiveness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
84.
85.
(1 ? x)BiFeO3 · xPbFe2/3W1/3O3 ((1 ? x)BFO · xPFWO) samples with 0 ≤ x ≤ 1 have been prepared by a standard ceramic processing technique and characterized by X-ray diffraction, dielectric measurements, and Mössbauer spectroscopy. The system has been shown to contain a continuous series of perovskite solid solutions. The solid solutions in the range 0 ≤ x < 0.32 have a rhombohedral structure and those with 0.32 ≤ x ≤ 1 have a cubic structure. Increasing the BFO content from 0 to 40% leads to rapid degradation of the dielectric permittivity peak that occurs at 180 K in PFWO and is due to the relaxor behavior of this component. At higher BFO concentrations, the electrical conductivity of the solid solutions increases by about two orders of magnitude. The temperature dependences of permittivity for the samples containing ~80% BFO have prominent maxima around 430 and 520 K, whose position is frequency-independent. The solid solutions exhibited no piezoelectric or pyroelectric effect, probably because they were insufficiently poled in a field of 10 kV/cm at 300 K. At higher electric field intensities, the samples experienced breakdown.  相似文献   
86.
We report the fabrication process as well as material and electrical characterization of ultra thin body (UTB) thin film transistors (TFTs) for stackable nonvolatile memories by using in situ phosphorous doped low-temperature polysilicon followed by the chemical mechanical polishing (CMP) process. The resulting polysilicon film is about 13 nm thick with approximately 1019 cm−3 doping. Root mean square surface roughness below 1 nm is achieved. Metal nanocrystals and high-k dielectric are selected for storage nodes and tunneling barriers to achieve low operating voltages. The number density and average diameter of nanocrystals embedded in the gate stack are 7.5 × 1011 cm−2 and 5.8 nm, respectively. Furthermore, scanning transmission electron microscopy (STEM), convergent beam electron diffraction (CBED) and electron energy loss spectroscopy (EELS) are performed for material characterization. The dielectric constant of the (Ti, Dy)xOy film is 35, and the off-state leakage current at −1 V bias and 2.8 nm equivalent oxide thickness is 5 × 10−7 A/cm2. We obtain a memory window of about 0.95 V with ±6 V program/erase voltages. Our results show that UTB TFT is a promising candidate for the three-dimensional integration in high-density nonvolatile memory applications.  相似文献   
87.
Atomic transport in the presence of a temperature gradient, commonly known as thermotransport or the thermomigration phenomenon, was simulated for U-Zr alloys using a phase-field model derived from irreversible thermodynamics. The free energy of the U-Zr system, a necessary ingredient for the phase-field-model, was directly incorporated from the available thermodynamic database. Kinetic parameters such as atomic mobility and heat of transport terms were obtained from experimental values reported in the literature. The model was applied to a single-phase (bcc-γ phase) alloy and to a diffusion couple consisting of two single-phase (bcc-γ phase) alloys of different compositions, both subjected to a constant temperature gradient. Constituent redistribution in the absence and presence of a compositional gradient was examined. An enrichment of Zr with a corresponding depletion of U was observed at the hot end of the initially homogeneous single-phase alloy. A similar atomic transport behavior was observed in the diffusion couple, where the magnitude and direction of the final composition gradient was dictated by the combined influence of atomic mobility and heat of transport terms.  相似文献   
88.
The suppression of apoptosis may contribute to the carcinogenicity of the peroxisome proliferators (PPs), a class of non-genotoxic rodent hepatocarcinogens. Our previous work demonstrated that the PP nafenopin suppressed both spontaneous and transforming growth factor beta1 (TGFbeta1)-induced hepatocyte apoptosis both in vivo and in vitro. Here, we extend these observations by demonstrating the ability of nafenopin to suppress apoptosis induced by other major candidates for the signalling of cell death in the liver. Treatment of rat or mouse hepatocyte monolayers with TGFbeta1 or the DNA damaging drugs etoposide or hydroxyurea induced high levels of apoptosis. Western blot analysis did not support a role for either p53 or p21waf1 in etoposide-induced apoptosis in rat hepatocytes. Treatment of mouse hepatocytes with an agonistic anti-Fas antibody also resulted in an induction of high levels of apoptosis. Pre-addition and continued exposure to nafenopin suppressed apoptosis induced by all three stimuli. Overall, our studies demonstrate that the ability of nafenopin to protect hepatocytes from apoptosis is not restricted to species or apoptotic stimulus. It is possible, therefore, that the PPs may suppress apoptosis by acting on diverse signalling pathways. However, it seems more likely that nafenopin suppresses hepatocyte apoptosis elicited by each death stimulus by impinging on a core apoptotic mechanism.  相似文献   
89.
There is growing demand for functional food products enriched with long chain omega-3 polyunsaturated fatty acids (LCω3PUFA). Nanoemulsions, systems with extremely small droplet sizes have been shown to increase LCω3PUFA bioavailability. However, nanoemulsion creation and processing methods may impact on the oxidative stability of these systems. The present systematic review collates information from studies that evaluated the oxidative stability of LCω3PUFA nanoemulsions suitable for use in functional foods. The systematic search identified seventeen articles published during the last 10 years. Researchers used a range of surfactants and antioxidants to create systems which were evaluated from 7 to 100 days of storage.

Nanoemulsions were created using synthetic and natural emulsifiers, with natural sources offering equivalent or increased oxidative stability compared to synthetic sources, which is useful as consumers are demanding natural, cleaner label food products. Equivalent vegetarian sources of LCω3PUFA found in fish oils such as algal oils are promising as they provide direct sources without the need for conversion in the human metabolic pathway. Quillaja saponin is a promising natural emulsifier that can produce nanoemulsion systems with equivalent/increased oxidative stability in comparison to other emulsifiers. Further studies to evaluate the oxidative stability of quillaja saponin nanoemulsions combined with algal sources of LCω3PUFA are warranted.  相似文献   

90.
The mucin MUC1 is overexpressed and aberrantly glycosylated by many epithelial cancer cells manifested by truncated O‐linked saccharides. Although tumor‐associated MUC1 has generated considerable attention because of its potential for the development of a therapeutic cancer vaccine, it has been difficult to design constructs that consistently induce cytotoxic T‐lymphocytes (CTLs) and ADCC‐mediating antibodies specific for the tumor form of MUC1. We have designed, chemically synthesized, and immunologically examined vaccine candidates each composed of a glycopeptide derived from MUC1, a promiscuous Thelper peptide, and a TLR2 (Pam3CysSK4) or TLR9 (CpG‐ODN 1826) agonist. It was found that the Pam3CysSK4‐containing compound elicits more potent antigenic and cellular immune responses, resulting in a therapeutic effect in a mouse model of mammary cancer. It is thus shown, for the first time, that the nature of an inbuilt adjuvant of a tripartite vaccine can significantly impact the quality of immune responses elicited against a tumor‐associated glycopeptide. The unique adjuvant properties of Pam3CysSK4, which can reduce the suppressive function of regulatory T cells and enhance the cytotoxicity of tumor‐specific CTLs, are likely responsible for the superior properties of the vaccine candidate 1 .  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