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   2915篇
  免费   113篇
  国内免费   14篇
电工技术   214篇
综合类   10篇
化学工业   888篇
金属工艺   104篇
机械仪表   72篇
建筑科学   61篇
能源动力   159篇
轻工业   316篇
水利工程   2篇
石油天然气   4篇
无线电   144篇
一般工业技术   633篇
冶金工业   118篇
原子能技术   79篇
自动化技术   238篇
  2024年   5篇
  2023年   18篇
  2022年   38篇
  2021年   53篇
  2020年   34篇
  2019年   43篇
  2018年   57篇
  2017年   51篇
  2016年   61篇
  2015年   53篇
  2014年   96篇
  2013年   228篇
  2012年   137篇
  2011年   221篇
  2010年   163篇
  2009年   178篇
  2008年   186篇
  2007年   156篇
  2006年   141篇
  2005年   133篇
  2004年   115篇
  2003年   104篇
  2002年   101篇
  2001年   69篇
  2000年   53篇
  1999年   45篇
  1998年   38篇
  1997年   46篇
  1996年   39篇
  1995年   33篇
  1994年   52篇
  1993年   34篇
  1992年   27篇
  1991年   19篇
  1990年   20篇
  1989年   20篇
  1988年   20篇
  1987年   16篇
  1986年   11篇
  1985年   19篇
  1984年   11篇
  1983年   23篇
  1982年   15篇
  1981年   8篇
  1980年   6篇
  1979年   7篇
  1978年   7篇
  1977年   7篇
  1976年   9篇
  1975年   6篇
排序方式: 共有3042条查询结果,搜索用时 15 毫秒
101.
Metallurgical and Materials Transactions B - Normal spectral emissivity of molten Cu-Fe alloy with different compositions was measured at the wavelength of 807 nm using an electromagnetic...  相似文献   
102.
Metallurgical and Materials Transactions B - Evolution of TiS in composition and morphology as well as the change in size distribution of TiS and TiN in Fe-40 masspctNi austenitic alloy during...  相似文献   
103.
We identified 22 genes from Aspergillus oryzae that are preferentially expressed in membrane-surface liquid culture (MSLC), among which Ser/Thr protein kinase (aopk1) and phosphatase (aoppt) genes were cloned. We also revealed that aopk1 encodes a protein with an N-terminal sequence 150 amino acid residues longer than that predicted from the registered sequence in GenBank.  相似文献   
104.
We prepared five mutant lysozymes in which glycines whose dihedralangles are located in the region of the left-handed helix, Gly49,Gly67, Gly71, Gly102 and Gly117, were mutated to an alanineresidue. From analyses of their thermal stabilities using differentialscanning calorimetry, most of them were more destabilized thanthe native lysozyme, except for the G102A mutant, which hasa stability similar to that of the native lysozyme at pH 2.7.As for the destabilized mutant lysozymes, their X-ray crystallographicanalyses showed that their global structures did not changebut that the local structures changed slightly. By examiningthe dihedral angles at the mutation sites based on X-ray crystallographicresults, it was found that the dihedral angles at these mutationsites tended to adopt favorable values in a Ramachandran plotand that the extent and direction of their shifts from the originalvalue had similar tendencies. Therefore, the change in dihedralangles may be the cause of the slight local structural changesaround the mutation site. On the other hand, regarding the mutationof G102A, the global structure was almost identical with thatof the native structure but the local structure was drasticallychanged. Therefore, it was suggested that the drastic localconformational change might be effective in releasing the unfavorableinteraction of the native state at the mutation site.  相似文献   
105.
Occurrence and sources of perfluorinated surfactants in rivers in Japan   总被引:4,自引:0,他引:4  
We analyzed perfluorinated surfactants (PFSs) in 20 river samples and 5 wastewater secondary effluent samples in Japan to reveal their occurrence and sources. Nine PFS species were determined: perfluorooctanesulfonate (PFOS), perfluorooctane sulfonamide (FOSA), perfluoroheptanoate (PFHpA), perfluorooctanoate (PFOA), perfluorononanoate (PFNA), perfluorodecanoate (PFDA), perfluoroundecanoate (PFUA), perfluorododecanoate (PFDDA), and perfluorotridecanoate (PFTDA). PFSs were detected in all rivers, revealing nationwide contamination of rivers. In particular, 11 out of 20 river samples exceeded New Jersey guidance for PFOA in drinking water (40 ng/L). PFOS, PFHpA, PFOA, and PFNA were major species in Japan. Concentrations of PFOS, PFHpA, and PFNA in rivers were strongly correlated with population density, suggesting that the chemicals were derived from urban activities. PFOA showed a significant but weak correlation. We used crotamiton, a marker of sewage effluent, for further source analysis. Concentrations of PFOS, PFHpA, and PFNAwere strongly correlated with those of crotamiton, and plots of secondary effluents fell near the regression lines of rivers, indicating that the PFOS, PFHpA, and PFNA in rivers were derived from sewage effluent. On the other hand, PFOA was found at remarkably high levels (54-192 ng/L) in seven river samples containing low levels of crotamiton, suggesting that it was derived from nonsewage point sources, as well as sewage effluent. The total fluxes of sewage-derived PFOS, PFHpA, PFOA, and PFNA from Japan were estimated to be 3.6, 2.6, 5.6, and 2.6 t/year, respectively. This is the first report to identify PFOA in several rivers, derived from nonsewage point sources, by using a marker of sewage effluent.  相似文献   
106.
浸没式光刻的优势和可行性   总被引:3,自引:2,他引:3  
浸没式光刻通过高折射率的液体充入透镜底部和片子之间的空间使光学系统的数值孔径具有显著的优势。在193nm曝光系统中,水(折射率为1.44)被选作最佳的浸入液体。通过成像模拟,现已证明ArF穴193nm雪浸没式光刻(NA=1.05~1.23)与F2穴157nm雪干法穴NA=0.85~0.93雪光刻具有几乎相同的成像性能。结合流体力学和热模拟结果,讨论了ArF浸没式曝光设备的优势和可行性。  相似文献   
107.
Epithelial ovarian cancer (EOC) is the most lethal gynecologic malignancy and has a unique metastatic route using ascites, known as the transcoelomic root. However, studies on ascites and contained cellular components have not yet been sufficiently clarified. In this review, we focus on the significance of accumulating ascites, contained EOC cells in the form of spheroids, and interaction with non-malignant host cells. To become resistant against anoikis, EOC cells form spheroids in ascites, where epithelial-to-mesenchymal transition stimulated by transforming growth factor-β can be a key pathway. As spheroids form, EOC cells are also gaining the ability to attach and invade the peritoneum to induce intraperitoneal metastasis, as well as resistance to conventional chemotherapy. Recently, accumulating evidence suggests that EOC spheroids in ascites are composed of not only cancer cells, but also non-malignant cells existing with higher abundance than EOC cells in ascites, including macrophages, mesothelial cells, and lymphocytes. Moreover, hetero-cellular spheroids are demonstrated to form more aggregated spheroids and have higher adhesion ability for the mesothelial layer. To improve the poor prognosis, we need to elucidate the mechanisms of spheroid formation and interactions with non-malignant cells in ascites that are a unique tumor microenvironment for EOC.  相似文献   
108.
The normal spectral emissivity of molten Cu–Co alloy with different compositions was measured in the wavelength range of 780 nm to 920 nm and in the temperature range of 1430 K to 1770 K including the undercooled condition by an electromagnetic levitator superimposed with a static magnetic field. The emissivity was determined as the ratio of the radiance from a levitated molten Cu–Co droplet measured by a spectrometer to the radiance from a blackbody calculated by Planck’s law at a given temperature, where a static magnetic field of 2.5 T to 4.5 T was applied to the levitated droplet to suppress the surface oscillation and translational motion of the sample. We found little temperature dependence of the normal spectral emissivity of molten Cu–Co alloy. Concerning the composition dependence, the emissivity decreased markedly above 80 at%Cu and reached that of pure Cu, although its dependence was low between 20 at%Cu and 80 at%Cu. In addition, this composition dependence of the emissivity of molten Cu–Co alloy can be explained well by the Drude free-electron model.  相似文献   
109.
The electron transport capability of 4,4′-bis[N-(1-napthyl)-N-phenyl-amino] biphenyl (α-NPD) was investigated by fundamental physical measurements named as current–voltage (I–V) electrical property evaluation and displacement current measurement (DCM). In electron-dominated devices, the I–V characteristics of α-NPD were similar as that of (8-hydroxyquinolino) aluminum (Alq3) owing to their same order of electron mobilities. The interface of Al/LiF and α-NPD was proven to be an Ohmic contact through the evaluation of I–V characteristics at low bias regime (<3 V). And an electron injection barrier, 0.21 eV, at Al/LiF/α-NPD was obtained by extrapolating the temperature dependent I–V curves. The electron transport behavior in α-NPD film was further confirmed by DCM evaluations. Furthermore, an efficient white organic light emission device was successfully fabricated by using α-NPD as hole transport layer and electron transport layer, respectively.  相似文献   
110.
The present study examined odorant communication during acute illness provoked by injection of lipopolysaccharide (LPS; 100 μg/kg) and how these effects vary between prepubertal and adult conspecifics. Exposure to odor of LPS-treated adult male rats produced increased avoidance in both sexes of adults and prepubertal male partners. This response was not found when they were exposed to odor of LPS-treated prepubertal males. Even a 2.5-fold higher load of LPS in prepubertal males failed to produce aversive odor cues, suggesting that the difference in the odor is not a simple issue of dose/body volume. Both estradiol benzoate (20 μg/kg) and testosterone propionate (500 μg/kg), but not dihydrotestosterone (500 μg/kg) pretreatment in prepubertal males administered LPS restored the expression of aversive odor. These hormone treatments per se did not influence odor properties of prepubertal males, indicating that estrogen receptors may play a key regulatory role in the expression of aversive odor in LPS-treated prepubertal rats. These data suggest that the expression of sickness-related odor emerges through puberty, and likely involves a complex interaction between inflammation and sex steroids across development. (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