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   1250篇
  免费   63篇
  国内免费   5篇
电工技术   22篇
综合类   2篇
化学工业   252篇
金属工艺   20篇
机械仪表   34篇
建筑科学   41篇
能源动力   41篇
轻工业   158篇
水利工程   9篇
石油天然气   3篇
无线电   125篇
一般工业技术   241篇
冶金工业   179篇
原子能技术   11篇
自动化技术   180篇
  2023年   4篇
  2022年   25篇
  2021年   39篇
  2020年   20篇
  2019年   30篇
  2018年   53篇
  2017年   46篇
  2016年   37篇
  2015年   37篇
  2014年   53篇
  2013年   77篇
  2012年   76篇
  2011年   87篇
  2010年   65篇
  2009年   65篇
  2008年   70篇
  2007年   51篇
  2006年   47篇
  2005年   32篇
  2004年   40篇
  2003年   27篇
  2002年   26篇
  2001年   23篇
  2000年   19篇
  1999年   24篇
  1998年   62篇
  1997年   31篇
  1996年   28篇
  1995年   12篇
  1994年   13篇
  1993年   15篇
  1992年   6篇
  1991年   8篇
  1990年   4篇
  1989年   13篇
  1988年   4篇
  1987年   2篇
  1986年   5篇
  1985年   9篇
  1984年   4篇
  1983年   3篇
  1982年   2篇
  1981年   2篇
  1980年   2篇
  1978年   4篇
  1977年   2篇
  1976年   4篇
  1975年   3篇
  1962年   1篇
  1961年   1篇
排序方式: 共有1318条查询结果,搜索用时 15 毫秒
91.
While position emission tomography (PET) is an important molecular imaging technique for both preclinical research and clinical disease diagnosis/prognosis, chelator‐free radiolabeling has emerged as a promising alternative approach to label biomolecules or nanoprobes in a facile way. Herein, starting from bottom‐up synthesized WS2 nanoflakes, this study fabricates a unique type of WS2/WOx nanodots, which can function as inherent hard oxygen donor for stable radiolabeling with Zirconium‐89 isotope (89Zr). Upon simply mixing, 89Zr can be anchored on the surface of polyethylene glycol (PEG) modified WS2/WOx (WS2/WOx‐PEG) nanodots via a chelator‐free method with surprisingly high labeling yield and great stability. A higher degree of oxidation in the WS2/WOx‐PEG sample (WS2/WOx (0.4)) produces more electron pairs, which would be beneficial for chelator‐free labeling of 89Zr with higher yields, suggesting the importance of surface chemistry and particle composition to the efficiency of chelator‐free radiolabeling. Such 89Zr‐WS2/WOx (0.4)‐PEG nanodots are found to be an excellent PET contrast agent for in vivo imaging of tumors upon intravenous administration, or mapping of draining lymph nodes after local injection.  相似文献   
92.
The significance of the demonstration of a clonal B-cell population in gastric lymphoid infiltrates was investigated by analysis of immunoglobulin heavy chain (IgH) gene rearrangements using sensitive polymerase chain reactions, employing fluorescently labelled primers to target the FR3 and FR1 regions. Tissue blocks were studied showing different histological features (high-grade lymphoma, low-grade lymphoma, and chronic gastritis) from 12 gastrectomies for primary gastric lymphoma, together with blocks showing chronic gastritis from 13 cases of gastric adenocarcinoma and biopsies from 33 patients with active Helicobacter-associated chronic gastritis. Clonal IgH gene rearrangements were detected in lymphoma samples from eight of the gastrectomies for lymphoma (67 per cent). In four of these eight specimens, clonal rearrangements were also detectable in the samples showing only chronic gastritis. Three of 28 (11 per cent) informative biopsies showing active Helicobacter-associated chronic gastritis had detectable clonal populations. Clonal rearrangements were also demonstrated in two of eight (25 per cent) informative blocks showing chronic gastritis from eight gastrectomies for adenocarcinoma. It is concluded that the detection of a clonal population in a suspicious lymphoid infiltrate does not confirm the diagnosis of lymphoma, nor does the absence of such a population imply benignity.  相似文献   
93.
94.
We recently identified and characterized a novel murine gene, ENC-1, that is expressed primarily in the nervous system and encodes an actin-binding protein. To gain insight into a potential role for ENC-1 gene in the processes of cell differentiation and malignant transformation in the human nervous system, we first cloned and characterized the human homologue of ENC-1. The human ENC-1 gene appeared to be highly expressed in adult brain and spinal cord, and in a number of cell lines derived from nervous system tumors we detected low steady-state levels of ENC-1 mRNA. We used a neuroblastoma differentiation model, the retinoic acid-induced neuronal differentiation of SMS-KCNR cells, to study the regulation of the ENC-1 gene during neural crest cell differentiation. We found that the expression of ENC-1 increased dramatically in the differentiated SMS-KCNR cells as compared to control undifferentiated cells. These results suggest that ENC-1 expression plays a role during differentiation of neural crest cells and may be down regulated in neuroblastoma tumors.  相似文献   
95.
Despite the increased interest in and acceptance of religion by many psychologists and the American Psychological Association, it still appears that very few supervisees receive the proper training and supervision necessary to competently address religion in therapy. The authors identify supervisor actions that promote supervisee competence in this area by using 8 domains from C. D. Stoltenberg and U. Delworth's (1987) integrative developmental model as a template. A set of conceptual guidelines for developing supervisee competence in regard to working with religious clients and issues is presented along with examples of supervisor or therapist actions for each domain (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
96.
Extraction of rice brain oil using supercritical carbon dioxide and propane   总被引:1,自引:0,他引:1  
Extraction of rice bran lipids was performed using supercritical carbon dioxide (SC−CO2) and liquid propane. To provide a basis for extraction efficiency, accelerated solvent extraction with hexane was performed at 100°C and 10.34 MPa. Extraction pressure was varied for propane and SC−CO2 extractions. Also, the role of temperature in SC−CO2 extraction efficiency was investigated at 45,65, and 85°C. For the SC−CO2 experiments, extraction efficiencies were proportional to pressure and inversely proportional to temperature, and the maximal yield of oil achieved using SC−CO2 was 0.222±0.013 kg of oil extracted per kg of rice bran for conditions of 45°C and 35 MPa. The maximal yield achieved with propane was 0.224±0.016 kg of oil per kg of rice bran at 0.76 MPa and ambient temperature. The maximum extraction efficiencies of both SC−CO2 and propane were found to be significantly different from the hexane extraction baseline yield, which was 0.261±0.005 kg oil extracted per kg of rice bran. A simulated economic analysis was performed on the possibility of using SC−CO2 and propane extraction technologies to remove oil from rice bran generated in Mississippi. Although the economic analysis was based on the maximal extraction efficiency for each technology, neither process resulted in a positive rate of return on investment.  相似文献   
97.
We present a method for measuring the electrical conductivity of metallic materials that relies on the ratio of two loaded Q factors, QR/QX, with QR corresponding to a TE011-mode reference cavity made of aluminum, and QX the Q that results upon replacing the aluminum plate with the one fabricated from the material to be examined. Electrical conductivity is mathematically inferred from the ratio QR/QX where the loaded Q factors are measured by using the transmission-type method. Within a 3.0 percent accuracy, conductivities determined at 8.7 GHz for electrolytic copper (5.6 times 107 S/m) and brass (1.6 times 107 S/m) show to be in good agreement with those reported in the literature.  相似文献   
98.

Ultraviolet germicidal irradiation (UVGI) as an engineering control against infectious bioaerosols necessitates a clear understanding of environmental effects on inactivation rates. The response of aerosolized Serratia marcescens, Bacillus subtilis, and Mycobacterium parafortuitum to ultraviolet irradiation was assessed at different relative humidity (RH)levels in a 0.8 m3 completely-mixed chamber. Bioaerosol response was characterized by physical factors including median cell aerodynamic diameter and cell water sorption capacity and by natural decay and UV-induced inactivation rate as determined by direct microscopic counts and standard plate counts. All organisms tested sorbed water from the atmosphere at RH levels between 20% and 95% (up to 70% of dry cell mass at 95% RH); however, no concomitant change in median aerodynamic diameter in this same RH range was observed. Variations in ultraviolet spherical irradiance were minor and not statistically significant in the 20-95% RH range. Cell water sorption and inactivation response was similar for each of the pure cultures tested: when RH exceeded approximately 50%, sorption increased markedly and a sharp concurrent drop in UV-induced inactivation rate was observed.  相似文献   
99.
In this contribution we use computational tools to investigate the reaction of alcohol substrates with reactive nitrogen oxide species such as N2O3 and N2O4, leading to the formation of alkyl nitrites. These nitrites are interesting intermediates which can be processed to various valuable chemicals such as ketones/aldehydes and dimethyl oxalate while regenerating NO x . As such, NO x is used as an oxidation mediator, converting alcohol substrates to more reactive nitrites which can be selectively converted to more desired compounds, closing a catalytic cycle in NO x species.  相似文献   
100.
The homopolymerisation of styrene is studied in the presence of Y, USY and beta zeolites. High molecular weight polymers, in the range 0.7 × 106–1 × 106, are obtained in good yields. The activity of zeolite beta is only slightly increased by calcination of the as-synthesised material, pointing to an important role of the zeolite outer surface. The influence of the catalyst acidity upon the polymer molecular weight is evaluated by the use of dealuminated zeolites. This revised version was published online in July 2006 with corrections to the Cover Date.  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