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   3653篇
  免费   60篇
  国内免费   1篇
电工技术   201篇
综合类   5篇
化学工业   898篇
金属工艺   52篇
机械仪表   95篇
建筑科学   59篇
矿业工程   5篇
能源动力   90篇
轻工业   268篇
水利工程   7篇
石油天然气   9篇
无线电   430篇
一般工业技术   609篇
冶金工业   747篇
原子能技术   85篇
自动化技术   154篇
  2023年   13篇
  2022年   28篇
  2021年   48篇
  2020年   20篇
  2019年   34篇
  2018年   36篇
  2017年   46篇
  2016年   39篇
  2015年   37篇
  2014年   60篇
  2013年   144篇
  2012年   101篇
  2011年   134篇
  2010年   112篇
  2009年   111篇
  2008年   136篇
  2007年   107篇
  2006年   108篇
  2005年   101篇
  2004年   106篇
  2003年   110篇
  2002年   107篇
  2001年   81篇
  2000年   58篇
  1999年   94篇
  1998年   318篇
  1997年   203篇
  1996年   145篇
  1995年   119篇
  1994年   83篇
  1993年   79篇
  1992年   67篇
  1991年   43篇
  1990年   46篇
  1989年   55篇
  1988年   46篇
  1987年   35篇
  1986年   46篇
  1985年   44篇
  1984年   37篇
  1983年   57篇
  1982年   45篇
  1981年   45篇
  1980年   28篇
  1979年   41篇
  1978年   27篇
  1977年   38篇
  1976年   44篇
  1975年   13篇
  1973年   10篇
排序方式: 共有3714条查询结果,搜索用时 62 毫秒
1.
2.
Metallothionein (MT) synthesis induced by the inflammatory cytokines, interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF), was studied in vivo. Administration of recombinant human IL-6 or TNF to rats caused the acute phase responses including rapid decreases in plasma zinc (Zn), and increases in plasma copper (Cu) and ceruloplasmin. Hepatic concentration of MT-I, one of MT isoforms, began to increase within 3 h after the injection of IL-6 or TNF. In IL-6-treated rats, MT-I concentration in liver reached a maximum level at 12 h and decreased with a transient rebound, whereas, in TNF-treated rats, a high level of MT-I lasted for about 48 h. MT-II, the other MT isoform, was induced more than MT-I in liver by both cytokines. MT-I was also induced in lung and heart by TNF, but little by IL-6. The data suggest that IL-6 may be responsible for MT synthesis in liver, whereas TNF may be responsible not only in liver but also in lung and heart. Furthermore plasma concentration of MT did not always reflect the enhanced concentration of MT by TNF and IL-6 in liver, suggesting involvement of many factors influencing plasma MT levels. The interrelation between IL-6 and TNF for MT synthesis has also been discussed.  相似文献   
3.
A new lateral MOS-gated thyristor, called the Base-Current-Controlled Thyristor, is described. This device is designed so that most holes at the on-stage reach the P base through the floating P+ region adjacent to the P base and the on-state MOSFET. At the turn-off stage, the interruption of the hole current to the P base due to switching off the above MOSFET occurs simultaneously with the conventional turn-off operation. The concept of this device is verified experimentally by using the fabricated lateral device with the external MOSFET. This device exhibits a better trade-off relation between the on-state voltage and the turn-off time compared uith the conventional MOS-gated thyristor  相似文献   
4.
The copreheat-treatment of non-fusible and slightly fusible coals with A240 and hydrogenated A240 under high temperature-short contact-time conditions around 500 °C has been examined in an attempt to produce a formed coke with better anisotropic development. These conditions shortened the copreheat-treatment time and provided better anisotropic development in the resultant coke after carbonization. Effectiveness of short contact-time has been discussed in terms of the extent of depolymerization of coal molecules suitable for anisotropic development, this being related to coal liquefaction under similar conditions.  相似文献   
5.
The diffusional behavior of multi-arm star-shaped p(tBMA) was investigated in a concentration range from dilute to semidilute region with 1H pulsed field gradient spin-echo NMR (PFGSE-NMR). An 142-arm star-shaped p(tBMA) showed two diffusional mode, which reflected the coexistence of liquid ordering phase and liquid phase near the ordering transition. On the other hand, for star-shaped p(tBMA) with 55 arms showed a single diffusional relaxation in all concentration ranges during observation time. In the semidilute region, the relationship between the diffusion coefficient against the polymer concentration was affected strongly not only the arm number but also liquid ordering structure.  相似文献   
6.
BACKGROUND: The biotransformation of sesquiterpenoids, which are a large class of naturally occurring compounds, using microorganisms as a biocatalyst to produce useful novel organic compounds was investigated. The biotransformation of sesquiterpenoids, (+)‐aromadendrene ( 1 ), (−)‐alloaromadendrene ( 2 ) and (+)‐ledene ( 3 ) has been investigated using Aspergillus wentii as a biocatalyst. Results: Compound 1 was converted to (−)‐(10S,11S)‐10,13,14‐trihydroxyaromadendrane ( 4 ). Compound 2 was converted to (+)‐(1S,11S)‐1,13‐dihydroxyaromadendrene ( 5 ) and (−)‐5,11‐epoxycadin‐1(10)‐en‐14‐ol ( 6 ). Compound 3 was converted to compound 6 , (+)‐(10R,11S)‐10,13‐dihydroxyaromadendr‐1‐ene ( 7 ) and (+)‐(10S,11S)‐10,13‐dihydroxyaromadendr‐1‐ene ( 8 ). The structure of the metabolic products has been elucidated on the basis of their spectral data. CONCLUSION: Compound 1 gave only one product that was hydroxylated at C‐10, C‐13 and C‐14. By contrast, compounds 2 and 3 gave a number of products, one of which was common. The differences in oxidation of 1–3 are due to the configuration of the C‐1 position. Compounds 4–8 were new compounds. Copyright © 2008 Society of Chemical Industry  相似文献   
7.
A transceiver PIC consisting of a DFB-LD, a receiver PD and a Y-shaped branch waveguides is realized by in-plane bandgap energy controlled selective MOVPE. Both active and passive core layers are formed in one step selective growth, and complicated fabrication procedure is no longer required. More than 1 mW fiber coupled power and 7 GHz receiver bandwidth are obtained. The modulation and detection operations at 500 Mb/s are successfully demonstrated.  相似文献   
8.
9.
Three phase partitioning (TPP) uses t-butanol and ammonium sulfate to precipitate enzymes and proteins from aqueous solutions. The method is useful both upstream with crude samples and downstream where a scaleable simple step is needed. About 25 enzymes and proteins have been isolated by various laboratories using TPP-t-butanol. The relation of t-butanol used in TPP, with n-butanol used as an extraction agent from Morton's work, is reviewed. Some t-butanol appears bound to TPP-precipitated proteins which are actually protein-t-butanol coprecipitates. They float above denser aqueous salts because bound t-butanol increases their buoyancy, similar to the behavior of many lipoproteins. On redissolving TPP-precipitated enzymes, total and specific activities usually are regained and sometimes increased. Sulfate ion-in large concentrations-likely exerts itself through its kosmotropic action as in conventional salting out. t-Butanol likewise appears to be a kosmotrope and crowding agent at room temperature or above, whereas C1 and C2 cosolvents (e.g., ethanol) do not so behave except at near or below zero temperatures. However, kosmotropy is not the entire origin of TPP, nor probably of conventional salting out. Electrostatic forces, capacity to force protein conformation tightening and protein hydration shifts, also contribute. Electrostatic forces, and the tendency for salt ions to bind and tighten protein molecule conformation, are indicated by the sharp pH dependency of both conventional salting out and TPP, around pH regions where proteins undergo conformation changes. Sulfate anion is densely-perhaps extraordinarily-hydrated, adding much to its effective size, and therefore it has a tendency to crowd or exclude proteins, when sulfate concentrations are in the 0.5 to 3 M range.  相似文献   
10.
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