全文获取类型
收费全文 | 248510篇 |
免费 | 1920篇 |
国内免费 | 264篇 |
专业分类
电工技术 | 4039篇 |
综合类 | 90篇 |
化学工业 | 39984篇 |
金属工艺 | 15145篇 |
机械仪表 | 10068篇 |
建筑科学 | 4187篇 |
矿业工程 | 3757篇 |
能源动力 | 3874篇 |
轻工业 | 9713篇 |
水利工程 | 4092篇 |
石油天然气 | 13006篇 |
武器工业 | 28篇 |
无线电 | 20186篇 |
一般工业技术 | 62774篇 |
冶金工业 | 32185篇 |
原子能技术 | 11135篇 |
自动化技术 | 16431篇 |
出版年
2021年 | 2750篇 |
2019年 | 2734篇 |
2018年 | 5432篇 |
2017年 | 5716篇 |
2016年 | 6049篇 |
2015年 | 3055篇 |
2014年 | 5326篇 |
2013年 | 10089篇 |
2012年 | 7309篇 |
2011年 | 8942篇 |
2010年 | 7298篇 |
2009年 | 8111篇 |
2008年 | 8176篇 |
2007年 | 7859篇 |
2006年 | 6367篇 |
2005年 | 5564篇 |
2004年 | 5481篇 |
2003年 | 5300篇 |
2002年 | 5134篇 |
2001年 | 4949篇 |
2000年 | 4941篇 |
1999年 | 4256篇 |
1998年 | 7190篇 |
1997年 | 5846篇 |
1996年 | 4425篇 |
1995年 | 3660篇 |
1994年 | 3431篇 |
1993年 | 3628篇 |
1992年 | 3217篇 |
1991年 | 3359篇 |
1990年 | 3482篇 |
1989年 | 3369篇 |
1988年 | 3268篇 |
1987年 | 3261篇 |
1986年 | 3157篇 |
1985年 | 3317篇 |
1984年 | 3252篇 |
1983年 | 3149篇 |
1982年 | 2994篇 |
1981年 | 3045篇 |
1980年 | 3071篇 |
1979年 | 3257篇 |
1978年 | 3490篇 |
1977年 | 3461篇 |
1976年 | 3914篇 |
1975年 | 3209篇 |
1974年 | 3293篇 |
1973年 | 3342篇 |
1972年 | 2987篇 |
1971年 | 2747篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
961.
The program HBexplore is a new tool for identifying and analysing H-bonding patterns in biological macromolecules. It selects all potential H-bonds according to geometrical criteria. The H-bond table can then be subjected to further automatic or interactive analysis tools. These tools include the calculation of mean values and distributions of geometrical H-bond parameters for parts of a single structure, for complete single structures and for structure sets, the classification of each H-bond according to the participation of backbone, side chain or base, ligand and water parts of nucleic acids or proteins, identification of Watson-Crick nucleotide pairs and of H-bonded pairs of equal nucleotides, the calculation of the mean number of H-bonds per residue, and of the fraction of potential donor and acceptor atoms involved in H-bonds. HBexplore further generates automatically a H-bond residue interaction table. This table lists for all residues of the structure the other residues, ligands or water molecules directly connected via a H-bond. By means of a binary tree search algorithm, this table is then converted into a H-bond cluster table. Clusters are understood here as an uninterrupted network of H-bonded residues. For nucleic acids, secondary structures and tertiary interactions are automatically derived from the H-bonding pattern. HBexplore is applied to two example RNA structures: a pseudoknot and a hairpin. It provides a comprehensive listing of individual H-bonds and statistical information for larger structure sets. In addition, it can identify interesting new H-bond motifs. One example is a pentanucleotide base-base H-bond interaction motif in the RNA pseudoknot. HBexplore is intended to contribute both to the elucidation of general principles of the architecture of biological macromolecules, and to the prediction and refinement of single structures. 相似文献
962.
N. V. Filimonova A. B. Ivanov Z. V. Tret'yakova 《Refractories and Industrial Ceramics》1996,37(10):348-351
Inflammation of a mixture of Furnon-3KhP refractory mortar prepared using a binary reducer consisting of metallic Al and Mg powders is considered. It is shown that the inflammation temperature can be decreased by 100 – 150°C. Mechanical characteristics of refractory bricks joined by the mortar are determined.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 10, pp. 16 – 19, October, 1996. 相似文献
963.
Polytechnic Institute, Tomsk. Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 2, pp. 6–11, March–April, 1993. 相似文献
964.
965.
V. A. Budarin 《Journal of Engineering Physics and Thermophysics》1995,68(2):182-185
The scheme of an experiment and certain results of the interaction of a free air vortex tube with a surface are considered. A solution of a differential equation for a plane cross section of a quasisolid tubular vortex core whose density varies according to a polytrope law is analyzed.Odessa Polytechnic University. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 2, pp. 212–216, March–April, 1995. 相似文献
966.
V. P. Naumenko 《Strength of Materials》1996,28(1):10-18
The adoption of unified fracture mechanics terminology (UFMT) will promote efficient communication between specialists in different fields of fracture research, harmonization of national and international standards relating to fracture mechanics, and last but not least improvement of the existing methodology for teaching and education in fatigue and fracture. In this paper the definitions of some basic and related terms included in different standards on fracture mechanics terminology are confronted with one another. Alternative definitions of the same terms are offered. By this strategy the author tries to show that the definitions of basic and related terms appropriate for the UFMT should emerge as a consequence of harmonizing a crack model with an actual crack and then both taken together with a fracture model, laboratory test methods, and failure assessment codes.Published in Problemy Prochonsti, No. 1, pp. 17–29, January, 1996.This paper is published as a matter of discussion. 相似文献
967.
A Zemtsov GS Cameron CA Bradley V Montalvo-Lugo F Mattioli 《Canadian Metallurgical Quarterly》1994,308(6):365-369
Phosphocreatine molecules (PCR) in skin regenerate adenosine triphosphate and help cutaneous tissue survive ischemia associated with skin flaps, grafts, and hair transplantation procedures. In addition, PCR concentration in psoriasis is elevated many times above normal, indicating either overproduction of PCR by mitochondrial creatine phosphokinase (CPK) enzymes or a defect in cytosol CPK enzymatic activity. Skin CPK isoenzymes, before this study, have not been identified. Herein, for the first time, cytosol CPK enzymatic activity was measured in normal and psoriatic, involved and uninvolved skin, skin tumors, and mouse skin and keratinocyte cell cultures. Creatine phosphokinase MM is the major isoenzyme in normal, uninvolved psoriatic and mouse skin. Total CPK enzymatic activity was increased in psoriasis and skin tumors. These data clearly indicate that increased PCR concentration in a psoriatic skin is not a result of decreased cytosol CPK enzymatic activity. 相似文献
968.
The concept of moving surface boundary-layer control, as applied to a Joukowsky airfoil, is investigated through a planned
experimental programme complemented by numerical studies. The moving surface was provided by rotating cylinders located at
the leading edge and/or trailing edge as well as top surface of the airfoil. Results suggest that the concept is quite promising,
leading to a substantial increase in lift and a delay in stall. Depending on the performance desired, appropriate combinations
of cylinder geometry, location and speed can be selected to obtain favourable results over a wide range of angle of attack.
Next, effectiveness of the concept in reducing drag of bluff bodies such as a two-dimensional flat plate at large angles of
attack, rectangular prisms and three-dimensional models of trucks is assessed through an extensive wind tunnel test-programme.
Results show that injection of momentum through moving surfaces, achieved here by introduction of bearing-mounted, motordriven,
hollow cylinders, can significantly delay separation of the boundary-layer and reduce the pressure drag. The momentum injection
procedure also proved effective in arresting wind-induced vortex resonance and galloping type of instabilities. A flow visualization
study, conducted in a closed-circuit water tunnel using slit lighting and polyvinyl choride tracer particles, adds to the
wind-tunnel and numerical investigations. It shows, rather dramatically, the effectiveness of the moving surface boundary-layer
control (MSBC).
The Sabita Chaudhury Memorial Lecture
The models were fabricated in the Mechanical Engineering Workshop. The assistance of M/s E Abell, P Hurren and D Camp in the
design and construction of the models is gratefully acknowledged. The investigation was supported by the Natural Sciences
and Engineering Research Council of Canada, Grant No. A-2181. 相似文献
969.
970.
Activation energy of electron-stimulated quenching of the photoluminescence of n-type porous silicon
The degradation of photoluminescence of porous silicon by kilovolt electrons and the mechanism and activation energy of this
process have been investigated. Quantitative relations between the integral intensity of the photoluminescence and the irradiation
dose and substrate temperature are obtained. The mechanism of the process is discussed and its activation energy is determined.
Pis’ma Zh. Tekh. Fiz. 23, 44–50 (September 26, 1997) 相似文献