全文获取类型
收费全文 | 2095篇 |
免费 | 61篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 51篇 |
综合类 | 3篇 |
化学工业 | 519篇 |
金属工艺 | 43篇 |
机械仪表 | 27篇 |
建筑科学 | 108篇 |
矿业工程 | 9篇 |
能源动力 | 32篇 |
轻工业 | 315篇 |
水利工程 | 14篇 |
石油天然气 | 2篇 |
无线电 | 125篇 |
一般工业技术 | 297篇 |
冶金工业 | 408篇 |
原子能技术 | 12篇 |
自动化技术 | 193篇 |
出版年
2022年 | 26篇 |
2021年 | 40篇 |
2020年 | 29篇 |
2019年 | 37篇 |
2018年 | 25篇 |
2017年 | 23篇 |
2016年 | 42篇 |
2015年 | 39篇 |
2014年 | 42篇 |
2013年 | 57篇 |
2012年 | 63篇 |
2011年 | 81篇 |
2010年 | 75篇 |
2009年 | 59篇 |
2008年 | 66篇 |
2007年 | 83篇 |
2006年 | 63篇 |
2005年 | 61篇 |
2004年 | 48篇 |
2003年 | 49篇 |
2002年 | 38篇 |
2001年 | 28篇 |
2000年 | 37篇 |
1999年 | 29篇 |
1998年 | 70篇 |
1997年 | 60篇 |
1996年 | 48篇 |
1995年 | 41篇 |
1994年 | 43篇 |
1993年 | 34篇 |
1992年 | 47篇 |
1991年 | 28篇 |
1990年 | 40篇 |
1989年 | 30篇 |
1988年 | 15篇 |
1987年 | 29篇 |
1986年 | 16篇 |
1985年 | 39篇 |
1984年 | 28篇 |
1983年 | 26篇 |
1982年 | 18篇 |
1981年 | 27篇 |
1980年 | 16篇 |
1979年 | 15篇 |
1978年 | 27篇 |
1977年 | 20篇 |
1976年 | 34篇 |
1974年 | 15篇 |
1972年 | 16篇 |
1970年 | 20篇 |
排序方式: 共有2158条查询结果,搜索用时 15 毫秒
101.
Rudolf F. Stark 《Computer-Aided Civil and Infrastructure Engineering》1992,7(2):161-175
Abstract: A local database manager (LDBM) is presented. It is a software development tool consisting of a set of easy-to-use in-core data management subroutines written in FORTRAN 77. One of the main motivations for the development of this LDBM was to enhance the eflcient use of core memory which seems to be obvious with respect to a PC programming environment. However, even on virtual machines, high performance achieved by minimizing page faults is strongly based on a sophisticated database management system (DBMS). In order to accomplish this objective, the LDBM allows the use of different data types according to the requirements of the actual situation and to the existing programming environment. Integer, short integer, real, double precision, complex, double complex and character data can be handled. Moreover, a two-level hierarchical data structure is used which groups related data in a different and more economic way rather than by means of increasing the number of levels in the DIMENSION statement. Of course, old, no longer used data may be deleted, leaving room for the allocation of new data. Using a technique of 'flexible garbage collection', i.e. the ensuing gap after the deletion of a data block is not automatically closed, the time consumed by the LDBM during a deletion operation is actually not affected by the length of data blocks. 相似文献
102.
103.
104.
T Jiang G Sweeney MT Rudolf A Klip A Traynor-Kaplan RY Tsien 《Canadian Metallurgical Quarterly》1998,273(18):11017-11024
Phosphoinositide 3-OH kinases and their products, D-3 phosphorylated phosphoinositides, are increasingly recognized as crucial elements in many signaling cascades. A reliable means to introduce these lipids into intact cells would be of great value for showing the physiological roles of this pathway and for testing the specificity of pharmacological inhibitors of the kinases. We have stereospecifically synthesized di-C8-PIP3/AM and di-C12-PIP3/AM, the heptakis(acetoxymethyl) esters of dioctanoyl- and dilauroylphosphatidylinositol 3,4,5-trisphosphate, in 14 steps from myo-inositol. The ability of these uncharged lipophilic derivatives to deliver phosphatidylinositol 3,4,5-trisphosphate across cell membranes was demonstrated on 3T3-L1 adipocytes and T84 colon carcinoma monolayers. Insulin stimulation of hexose uptake into adipocytes was inhibited by the kinase inhibitor wortmannin and was largely restored by di-C8-PIP3/AM, which had no effect in the absence of insulin. Thus phosphatidylinositol 3,4,5-trisphosphate or a metabolite was necessary but not sufficient for stimulation of hexose transport. In T84 epithelial monolayers, di-C12-PIP3/AM mimicked epidermal growth factor in inhibiting chloride secretion and potassium efflux, suggesting that phosphatidylinositol 3,4, 5-trisphosphate was sufficient to modulate these fluxes and mediate epidermal growth factor's action. 相似文献
105.
Directional reflectance properties of natural surfaces are very important in the interpretation of remotely sensed data. The analysis of multispectral scanner data shows a distinct dependence on scan angle, wavelength (0.4–1.1 μm), and classes (e.g., bare soil, vegetation). This relationship can be described by polynomials determined by regression methods. Atmospheric effects are computed with a simple model by parametrization of the multiple scattered skylight. The model permits a quick and sufficient estimation of the airlight, depending on the data collection conditions. Comparisons of the scanner data with the corresponding model yield the following results: The differences between airborne and ground measurements are due to atmospheric effects. The directional variation in brightness is mainly caused by the object itself with the exception of short wavelengths and/or a very low albedo. The hue shift of vegetation is essentially produced by the object and modified by the atmosphere. Taking into account the directional reflectance properties in a direction-dependent classification procedure results in an improvement of up to 20% in comparison with algorithms used so far. Quantitative relationships between ground measurements and radiation measurements by airborne sensors including atmospheric effects can be determined with the proposed methods. 相似文献
106.
H. Pfeiffer 《工业材料与腐蚀》1970,21(11):977-982
The oxidation behaviour of resistance heater alloys The prime condition for the use of metals as resistance heaters is their capability of forming compact and well adhering layers of scale of low permeability. In this context the composition of the alloy (in particular ferritic steels and representatives from the system NiCr) Play an important role in so far as oxidation has frequently a selective character, so that certain constituents may be depleted. Adhesion is also a function of the temperature regime (constant or cycling temperature during scale formation) be-cause these conditions may give rise to internal stresses in the covering layer. A tool for measuring stresses in the scale layer and thus adhesion is in particular the vibration method. In non-oxidising atmospheres increased chromium contents are generally useful; on the one hand they improve resistance to carburation and On the other hand they have a favourable influence on the resistance of nickel alloys in sulfidising atmospheres. 相似文献
107.
108.
109.
Dipl.-Ing.Dr. techn. Franz G. Rammerstorfer Dipl.-Ing. Dr. techn. Rudolf Beer 《Forschung im Ingenieurwesen》1976,42(5):168-172
Zusammenfassung Eine M?glichkeit, ohne Mehraufwand an Material oder Verwendung teurerer Werkstoffe das dynamische Verhalten oder die Tragf?higkeit
von Bauteilen zu verbessern, wird am Beispiel der Grundfrequenz- und Beullaststeigerung von Kreisplatten durch das Einpr?gen
von geeigneten Eigenspannungszust?nden dargelegt. Die Ergebnisse einer Optimierung solcher Eigenspannungsfelder werden dargestellt,
und die M?glichkeit der Erzeugung geeigneter Eigenspannungszust?nde wird an Hand eines Experiments nachgewiesen. 相似文献
110.
The chlorine and oxygen overpotential in dependence on the current density i (A cm?2) and on the temperature in the range of 15–75°C was measured at γ-MnO2 and β-PbO2 electrodes in concentrated water solutions of sodium chloride and perchlorate. From the measured values the experimental activation energy in dependence on overpotential was calculated and, for the temperature of 25°C, the constants of Tafel's equation (a,b) (α, io respectively) were evaluated. 相似文献