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   1275篇
  免费   51篇
  国内免费   4篇
化学   969篇
晶体学   3篇
力学   37篇
数学   202篇
物理学   119篇
  2023年   17篇
  2022年   31篇
  2021年   38篇
  2020年   27篇
  2019年   24篇
  2018年   15篇
  2017年   19篇
  2016年   43篇
  2015年   45篇
  2014年   39篇
  2013年   64篇
  2012年   75篇
  2011年   101篇
  2010年   70篇
  2009年   49篇
  2008年   70篇
  2007年   84篇
  2006年   74篇
  2005年   59篇
  2004年   58篇
  2003年   48篇
  2002年   45篇
  2001年   13篇
  2000年   9篇
  1999年   18篇
  1998年   9篇
  1997年   18篇
  1996年   11篇
  1995年   9篇
  1994年   6篇
  1993年   11篇
  1992年   8篇
  1990年   7篇
  1989年   4篇
  1988年   5篇
  1987年   6篇
  1986年   8篇
  1985年   7篇
  1984年   7篇
  1983年   6篇
  1982年   5篇
  1981年   6篇
  1979年   10篇
  1978年   5篇
  1976年   8篇
  1975年   3篇
  1974年   5篇
  1973年   5篇
  1972年   3篇
  1970年   3篇
排序方式: 共有1330条查询结果,搜索用时 10 毫秒
41.
One of the main applications in plasma physics concerns the energy production through thermo-nuclear fusion. The controlled fusion is achieved by magnetic confinement i.e., the plasma is confined into a toroidal domain (tokamak) under the action of huge magnetic fields. Several models exist for describing the evolution of strongly magnetized plasmas, most of them by neglecting the collisions between particles. The subject matter of this paper is to investigate the effect of large magnetic fields with respect to a collision mechanism. We consider here linear collision Boltzmann operators and derive, by averaging with respect to the fast cyclotronic motion due to strong magnetic forces, their effective collision kernels.  相似文献   
42.
This review summarizes research on many of the potential applications of photosensitized crosslinking of tissue proteins in surgery and current knowledge of the photochemical mechanisms underlying formation of the covalent protein–protein crosslinks involved. Initially developed to close wounds or reattach tissues, protein photocrosslinking has also been demonstrated to stiffen and strengthen tissues, decrease inflammatory responses and facilitate tissue bioengineering. These treatments appear to result largely from crosslinks within and between collagen molecules in tissue that typically form by an oxygen‐dependent mechanism. Surgical applications discussed include sealing wounds in skin, cornea and bowel; reattaching severed nerves, blood vessels and tendons; strengthening cornea and vein; reducing capsular contracture after breast implants; and regenerating joint cartilage.  相似文献   
43.
44.
45.
Athletes who illicitly use drugs to enhance their athletic performance are at risk of being banned from sports competitions. Consequently, some athletes may seek new doping methods that they expect to be capable of circumventing detection. With advances in gene transfer vector design and therapeutic gene transfer, and demonstrations of safety and therapeutic benefit in humans, there is an increased probability of the pursuit of gene doping by athletes. In anticipation of the potential for gene doping, assays have been established to directly detect complementary DNA of genes that are top candidates for use in doping, as well as vector control elements. The development of molecular assays that are capable of exposing gene doping in sports can serve as a deterrent and may also identify athletes who have illicitly used gene transfer for performance enhancement. PCR-based methods to detect foreign DNA with high reliability, sensitivity, and specificity include TaqMan real-time PCR, nested PCR, and internal threshold control PCR.  相似文献   
46.
The occurrence of di-(2-ethyhexyl)phthalate (DEHP), nonylphenol and nonyphenol mono- and diethoxylates (NPEs) and seven polychlorinated biphenyl (PCB) congeners in different types of sludge samples is reported. The analysis of these compounds was carried out by sonication-assisted extraction and analytical determination by gas chromatography coupled with a mass spectrometry detector, following a previously described method. The applicability of the method was tested by monitoring the organic pollutants in primary, secondary, mixed, and digested-dehydrated sludge samples from two wastewater treatment plants (WWTPs) based on aerobic and on anaerobic biological stabilization. The occurrence of these compounds in sewage sludge and the influence of sludge stabilization process on the further farmland application of the sludge were evaluated. DEHP and NPEs were detected in all analysed sludge samples from both WWTPs at concentration levels in the range of 22.3–601?mg?kg?1 and 136–2357?mg?kg?1 dm (dry matter), respectively. PCBs were detected in all types of sludge analysed from the anaerobic WWTP but was not detected in any sludge sample from the aerobic WWTP. Concentration levels of the sum of the seven PCBs congeners were up to 1.5?mg?kg?1 dm. The concentration of DEHP, sum of NPEs, and sum of the seven PCB congeners were higher than the limits fixed in the third draft of the future Sludge Directive for land application of sludge in the 67%, 100%, and 11% of samples from the anaerobic WWTP and in the 83%, 92%, and 0% of samples from the aerobic WWTP, respectively.  相似文献   
47.
48.
This work allowed the identification of major transformation products (TPs) of acetamiprid (ACTM) during Fenton process. Acetamiprid is a chloronicotinoid insecticide widely used around the world for its characteristics (high insecticidal activity, good systemic properties, suitable field stability, etc.). The degradation of the parent molecule and the identification of the main TPs were evaluated in different water matrices (demineralized water and real agro-food industrial wastewater). TPs of acetamiprid generated by Fenton experiments were monitored and identified by liquid chromatography quadrupole time-of-flight tandem mass spectrometry (LC–QTOF–MS/MS). Up to 14 TPs were characterized based on the accurate mass of the molecular ion and fragment ions obtained in both full-scan and MS/MS modes. Most of them were eliminated after 75 min of treatment time in demineralized water. However, in real agro-food industrial wastewater, most of them were eliminated at 90 min of treatment time, demonstrating the influence of the matrix composition on the studied compound degradation.  相似文献   
49.
Depth-resolved NADH autofluorescence images are shown to differentiate between normal and precancerous engineered tissues. An inverse power law behavior of the power spectral density (PSD) of these images is observed, indicating a self-affine organization of mitochondrial NADH at length scales 1-10 microm. Power exponents of the PSD functions vary significantly with tissue depth and precancerous state, giving insight into the morphological changes associated with precancerous lesions and providing substantial potential for noninvasive clinical diagnosis of squamous epithelial lesions and tumors.  相似文献   
50.
BACKGROUND AND PURPOSE: Functional neuroimaging can distinguish components of the pain experience associated with anticipation to pain from those associated with the experience of pain itself. Anticipation to pain is thought to increase the suffering of chronic pain patients. Inappropriate anxiety, of which anticipation is a component, is also a cause of disability. We present a pharmacological functional magnetic resonance imaging (fMRI) study in which we investigate the selective modulation by midazolam of brain activity associated with anticipation to pain compared to pain itself. METHODS: Eight right-handed male volunteers underwent fMRI combined with a thermal pain conditioning paradigm and midazolam (30 mug/kg) or saline administration on different occasions, with order randomized across volunteers. Volunteers learned to associate a colored light with either painful, hot stimulation or nonpainful, warm stimulation to the back of the left hand. RESULTS: Comparison of the period during thermal stimulation (pain-warm) revealed a network of brain activity commonly associated with noxious stimulation, including activities in the anterior cingulate cortex (ACC), the bilateral insular cortices (anterior and posterior), the thalamus, S1, the motor cortex, the brainstem, the prefrontal cortex and the cerebellum. Comparison of the periods preceding thermal stimulation (anticipation to pain-anticipation to warm) revealed activity principally in the ACC, the contralateral anterior insular cortex and the ipsilateral S2/posterior insula. Detected by a region-of-interest analysis, midazolam reduced the activity associated specifically with anticipation to pain while controlling for anticipation to warm. This was most significant in the contralateral anterior insula (P<.05). There were no significant drug effects on the activity associated with pain itself. CONCLUSION: In identifying a pharmacological effect on activity preceding but not during pain, we have successfully demonstrated an fMRI assay that can be used to study the action of anxiolytic agents in a relatively small cohort of humans.  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