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   5016篇
  免费   294篇
  国内免费   5篇
电工技术   51篇
综合类   14篇
化学工业   1430篇
金属工艺   167篇
机械仪表   133篇
建筑科学   111篇
矿业工程   33篇
能源动力   168篇
轻工业   647篇
水利工程   31篇
石油天然气   23篇
无线电   304篇
一般工业技术   1136篇
冶金工业   139篇
原子能技术   86篇
自动化技术   842篇
  2024年   15篇
  2023年   68篇
  2022年   134篇
  2021年   224篇
  2020年   140篇
  2019年   174篇
  2018年   231篇
  2017年   203篇
  2016年   227篇
  2015年   193篇
  2014年   291篇
  2013年   501篇
  2012年   288篇
  2011年   352篇
  2010年   334篇
  2009年   279篇
  2008年   202篇
  2007年   155篇
  2006年   119篇
  2005年   78篇
  2004年   78篇
  2003年   76篇
  2002年   75篇
  2001年   42篇
  2000年   50篇
  1999年   36篇
  1998年   34篇
  1997年   46篇
  1996年   38篇
  1995年   26篇
  1994年   35篇
  1993年   38篇
  1992年   25篇
  1991年   15篇
  1989年   20篇
  1988年   19篇
  1986年   14篇
  1985年   30篇
  1984年   30篇
  1983年   28篇
  1982年   30篇
  1981年   44篇
  1980年   30篇
  1979年   32篇
  1978年   25篇
  1977年   25篇
  1976年   39篇
  1975年   24篇
  1974年   16篇
  1973年   23篇
排序方式: 共有5315条查询结果,搜索用时 14 毫秒
101.
Brewer's spent grain (BSG) hydrolysates were used for l ‐(+)‐lactic acid (LA) fermentation by Lactobacillus rhamnosus ATCC 7469. In this study the effect of the addition of various amounts of thin stillage (TS) in BSG hydrolysate on LA fermentation parameters were evaluated. TS addition significantly increased utilization of glucose by up to 43.0%. In batch fermentation the highest LA concentration and volumetric productivity of 31.0 g/L, and 0.93 g/L/h, respectively, were obtained with the addition of 50% TS. L. rhamnosus cell viability also increased with the addition of 50% TS (by 2.4%). TS addition significantly increased free amino nitrogen concentration (by up to 209%) which is important for bacterial growth. A strong positive correlation between free amino nitrogen and LA concentration was noted. Compared with the results obtained in the batch fermentation (50% TS), significantly higher LA concentration, yield and volumetric productivity (54.8, 1.9 and 4.0%, respectively) were achieved in fed‐batch fermentation with glucose and TS addition. The results suggest that the combination of the by‐products of brewing and bioethanol industries could be suitable for LA production. Copyright © 2017 The Institute of Brewing & Distilling  相似文献   
102.
Hops contain large amounts of secondary metabolites, many of which have notable bioactive and sensory characteristics. Many of these properties are affected by the processing of raw hops into products. We studied the influence of high‐pressure processing (HPP) on the content and composition of secondary metabolites in hop homogenates prepared from fresh green cones of several Czech hop varieties. Homogenates contained more hop oils (27% on average) compared to dried hops. The composition of essential oils in homogenates after HPP showed a decrease in fatty acid methyl and thioesters fractions (80 and 100% respectively). Conversely, the number of other bioactive compounds from the group of resins and prenylflavonoids that remained in HPP homogenates was retained to a greater extent than in the dried hops. Low temperatures and an oxygen‐free atmosphere were effective conditions for the preservation of raw hops and hop products. Copyright © 2018 The Institute of Brewing & Distilling  相似文献   
103.
Sewing thread is one of the most important components of a sewn product that contributes significantly in the useful life of a product. Stitch class 504 is the one which is used in all types of sewn products. Its thread consumption is higher than class 300 and class 400. A mathematical model to predict the sewing thread consumption of stitch class 504 has been proposed in this paper. The model is based on the geometry of the stitch. The proposed model takes into account material thickness and stitch density. The model was validated by using 24 samples (with different material thickness and stitch densities). The accuracy of the model was found to be 99%. Sensitivity analysis revealed that stitch density has 62% effect and material thickness has 38% effect on thread consumption. The proposed model can predict the thread consumption accurately; therefore, it can be used for better estimation of required thread and encourage its better utilization in sewn product industry.  相似文献   
104.
An intermediate C-S-H phase, similar to the Assarsson's “Phase Z”, with basal spacing of 16Å formed when β-C2S or γ-C2S reacted with silicon dioxide (molar ratio CaO/SiO2 = 0.5–0.28) for 8 hours at 190°C under hydrothermal conditions. This intermediate C-S-H phase transformed to gyrolite upon prolonged hydrothermal treatment.  相似文献   
105.
Spěváček  J.  Schneider  B.  Baldrian  J.  Dybal  J.  Štokr  J. 《Polymer Bulletin》1983,9(10-11):495-501
Polymer Bulletin - Solutions of syndiotactic (s) poly (methyl methacrylate) (PMMA) and samples of solid s-PMMA prepared from these solutions were studied by NMR and infrared (IR) spectroscopy and...  相似文献   
106.
Whereas the logical apparatus used for formulation and solution of problems connected with the data base systems is mostly a 1st order logic, here a modified version (“T-system”) of Church's simple theory of types is used. It is shown that the T-system
1. (a) is a more adequate tool for analyzing natural language, which may be important when one builds up an abstract model of a fragment of reality and when one creates a suitable philosophy of data base systems;
2. (b) has greater expressive power than the 1st order systems, which enables, e.g. to distinguish between queries according to what is the structure of the required answer, and moreover, not to be restricted by the well-known limitations of the 1st order logics;
3. (c) is based on the notion of function as on the most fundamental notion, which makes it possible to deal more directly with functional dependencies and to exploit more universally the key importance of the attribute concept;
4. (d) by using the concept of construction offers a good tool for E-C mapping and for forming query languages that are more universal than the current ones.

The analysis of these properties of the T-system is accompanied by examples from the area of the data base systems theories; especially, a comparison with Codd's domain relational calculus and with Chen's and Pirotte's approaches is made. No problem of implementation is touched in this paper.  相似文献   

107.
A method is proposed for obtaining an upper bound for the displacement which can occur in a structure adapted to a given variable-repeated load. First, the exact formulation of the problem is presented which leads to a problem of optimal control. Then the differential constraints are neglected or replaced by algebraic conditions. The solution of the resulting linear programming problem supplies an upper bound to the exact elastic-plastic deflection. Further approximation can be introduced, if desired, which allows the decomposition of the problem into separate bounds to elastic and plastic parts of displacement.Numerical examples include a two-span continuous beam and a two-storey frame. The first was solved analytically, the second by means of a specially developed computer routine capable of evaluating the displacements at shakedown of arbitrary planar frames or trusses. The results obtained confirm the validity of the small displacement approach.  相似文献   
108.
109.
Male lambs, crossbred Merino × Ille de France, were fed a diet supplemented with 31 mg monensin or 32 mg lasalocid per kg of feed dry matter from an initial body weight of 23·6–23·9 kg to the slaughter weight of approximately 40 kg.

Carcass traits and meat quality were evaluated after slaughter; the values obtained were compared with those of the control group fed the same diet without the ionophore supplement.

There were few significant differences among the individual groups in carcass value, sensoric and technological properties of meat and of its composition. However, the lasalocid-fed group seemed to be somewhat better in muscling and in the composition of meat.  相似文献   

110.
Probiotic strain Lactobacillus plantarum L4 and strain Leuconostoc mesenteroides LMG 7954 were applied for the controlled fermentation of cabbage heads. The parameters of the controlled and spontaneous fermentations, including antimicrobial effect of cabbage brines obtained at the end of both fermentations, were monitored. To check out the influence of starter culture strains, 10 randomly chosen lactic acid bacteria, isolated at the end of controlled cabbage heads fermentation were identified by API 50 CHL test, and the presence of the probiotic culture was confirmed by Pulsed Field Gel Electrophoresis. The starter cultures applied for cabbage heads fermentation allowed lowering of NaCl concentrations from 4.0% to 2.5% (w/v), considerably accelerated fermentation process by 14 d, and improved the product quality. The produced sauerkraut heads are considered probiotic product as viable probiotic cells count in final product was higher than 10(6) colony-forming units (CFU) per gram of product. PRACTICAL APPLICATION: The results of this research could be applied in the production of fermented cabbage heads with added functional (probiotic) value and with lower NaCl concentration with expected shortened fermentation time. This could not only be of economic but also of ecological importance.  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