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41.
We report new measurements of the effective thermal conductivity Keff and relaxation time τ in dilute mixtures of3He in superfluid4He, with molar concentrationsX≤10−3. The temperature range extended fromT≈1.4 K toT
λ. Both Kcff and τ are found to agree with theoretical predictions, in contrast to previous experiments where significant differences
were observed. A new thermal conductivity cell design was used which almost completely eliminates extraneous volumes and surfaces,
and the earlier results are explained in relation to these design changes. 相似文献
42.
T Reck F K?ckerling C Schneider W Hohenberger 《Canadian Metallurgical Quarterly》1997,122(10):914-918
Morgagni hernias are the least common form of diaphragmatic hernias. Although they are congenital, most of them are not diagnosed until later in life. The indication for surgery is based on the patient's symptoms or on the radiological evidence of incarcerated tissue, and until quite recently involved a laparotomy or thoracotomy. Laparoscopy not only permits the suspected diagnosis to be confirmed--which is otherwise often difficult--but also makes it possible to close the hernia site by suturing. For improved security, the hernia site is augmented by fixing in place a non-absorbable mesh. The operative technique employed is described. 相似文献
43.
John C. Hart Gordon W. Lescinsky Daniel J. Sandin Thomas A. DeFanti Louis H. Kauffman 《The Visual computer》1993,9(7):346-355
The pipelined architecture and parallel organization of the AT&T Pixel Machine image computer are described and demonstrated with applications for the visualization of multidimensional fractals, particularly linear fractals and quaternion/ stacked Julia sets. Techniques for pushing the Pixel Machine to its peak abilities are described and apply to more recent parallel image computers as well. 相似文献
44.
Control law design for rotorcraft fly-by-wire systems normally attempts to decouple the angular responses using fixed-gain crossfeeds. This approach can lead to poor decoupling over the frequency range of pilot inputs and increase the load on the feedback loops. In order to improve the decoupling performance, dynamic crossfeeds should be adopted. Moreover, because of the large changes that occur in the aircraft dynamics due to small changes about the nominal design condition, especially for near-hovering flight, the crossfeed design must be ‘robust’. A new low-order matching method is presented here to design robust crossfeed compensators for multi-input, multi-output (MIMO) systems. The technique minimizes cross-coupling given an anticipated set of parameter variations for the range of flight conditions of concern. Results are presented in this paper of an analysis of the pitch/roll coupling of the UH-60 Black Hawk helicopter in near-hovering flight. A robust crossfeed is designed that shows significant improvement in decoupling perfomance and robustness over the fixed-gain or single point dynamic compensators. The design method and results are presented in an easily used graphical format that lends significant physical insight to the design procedure. This plant precompensation technique is an appropriate preliminary step to the design of robust feedback control laws for rotorcraft. 相似文献
45.
Industries in the US continue to lose ground in international competition. If IS is to help change that trend, it will have to become more creative. Creativity improvement programs are being introduced in other areas of the company— now is the time for IS organizations to follow suit. 相似文献
46.
Robotica is a computer-aided design package for robotic nmanipulators developed at the Coordinated Science Laboratory at the University of Illinois at Urbana- Champaign. The package is a collection of function definitions for the Mathematica symbolic mathematics program. Robotica can be used either with an X- Windows graphical user interface (GUI) on a Sun Workstation or as an included function definition file within Mathematica. The primary feature of Robotica is the ability to compute, symbolically or numerically, the kinematic and dynamic equations of arbitrary robot systems utilizing the standard Denevit-Hartenburg (DH) kinematic convention. Robotica also provides the ability to visualize these arbitrary manipulators using the X- Windows graphical interface to the Mathematica graphics routines. The paper looks at the usage of Robotica at the Air Force Institute of Technology, comments on the features of Robotica, and needs for improvement and suggestions for future development 相似文献
47.
MA Steller KJ Gurski M Murakami RW Daniel KV Shah E Celis A Sette EL Trimble RC Park FM Marincola 《Canadian Metallurgical Quarterly》1998,4(9):2103-2109
Human papillomavirus (HPV) infection has been causally associated with cervical cancer. We tested the effectiveness of an HLA-A*0201-restricted, HPV-16 E7 lipopeptide vaccine in eliciting cellular immune responses in vivo in women with refractory cervical cancer. In a nonrandomized Phase I clinical trial, 12 women expressing the HLA-A2 allele with refractory cervical or vaginal cancer were vaccinated with four E786-93 lipopeptide inoculations at 3-week intervals. HLA-A2 subtyping was also performed, and HPV typing was assessed on tumor specimens. Induction of epitope-specific CD8+ T-lymphocyte (CTL) responses was analyzed using peripheral blood leukapheresis specimens obtained before and after vaccination. CTL specificity was measured by IFN-gamma release assay using HLA-A*0201 matched target cells. Clinical responses were assessed by physical examination and radiographic images. All HLA-A*0201 patients were able to mount a cellular immune response to a control peptide. E786-93-specific CTLs were elicited in 4 of 10 evaluable HLA-A*0201 subjects before vaccination, 5 of 7 evaluable HLA-A*0201 patients after two vaccinations, and 2 of 3 evaluable HLA-A*0201 cultures after all four inoculations. Two of three evaluable patients' CTLs converted from unreactive to reactive after administration of all four inoculations. There were no clinical responses or treatment toxicities. The ability to generate specific cellular immune responses is retained in patients with advanced cervical cancer. Vaccination with a lipidated HPV peptide epitope appears capable of safely augmenting CTL reactivity. Although enhancements of cellular immune responses are needed to achieve therapeutic utility in advanced cervical cancer, this approach might prove useful in treating preinvasive disease. 相似文献
48.
Steeds M.W. Broschat S.L. Schneider J.B. 《Electromagnetic Compatibility, IEEE Transactions on》1996,38(2):181-187
Two conformal finite-difference time-domain (FDTD) methods are considered, the contour path (CPFDTD) method of Jurgens et al. (see IEEE Trans. Antennas Propagat., vol.40, p.357, 1992) and the overlapping grid (OGFDTD) method of Yee et al. (see IEEE Trans. Antennas Propagat., vol.40, p.1068, 1992). Both TE and TM scattering from a two-dimensional (2-D), perfectly conducting circular cylinder are used to test the accuracy of the methods for curved surfaces. Also, TE and TM scattering from a 2-D, perfectly-conducting rotated square cylinder are used to test the accuracy for corners and edges. It is shown that the conformal method proposed by Yee et al. provide significant improvement in accuracy over the original FDTD algorithm for most of the geometries studied. However, implementation becomes more difficult as the geometries become more complex. The conformal method proposed by Jurgens et al. provide significant improvement in accuracy as well for most of the geometries studied. However, improvement does not occur for the TM case when the square cylinder is not aligned properly with the grid. Implementation of the CPFDTD method is relatively straightforward. For the majority of the cases studied, the OGFDTD method is more accurate than the CPFDTD method 相似文献
49.
A novel discontinuous buffer system for DNA sequencing based on horizontal ultrathin-layer gel electrophoresis is described. The optimized system, named unbuffered stacking gel/discontinuous borate EDTA-buffer system, is composed of a 0.5 mm thick stacking gel, where standard sequencing reactions (1 microL volume) are easily loaded, and a 50 microns ultrathin running gel, where DNA fragments are separated. The novel discontinuous buffer system allows for sample concentration and efficient injection from the stacking gel into the capillary slab gel. Increased resolution, assessed by autoradiography, can be achieved within 25 min running time already over a 10.1 cm distance from the gel slot compared to the conventional gel system. An advantage of the new system is the capacity to resolve compressions in GC-rich regions, usually causing migrating artifacts in standard gels. The described system affords a major improvement in speed, resolution and reproducibility in DNA sequencing. 相似文献
50.
Daniel Walgraef Elias C. Aifantis 《International Journal of Engineering Science》1985,23(12):1351-1358
By distinguishing among mobile and immobile dislocations and operating within the framework of continuum mechanics it is possible to derive a set of partial differential equations of the diffusion-reaction type for the evolution of dislocation species. On examining the competition between gradient dependent terms modelling the motion of dislocations and nonlinear terms modelling their interactions, it is shown that stable solutions are possible. The wavelength turns out to be a material property in agreement with observations. The discussion is limited to one dimension, that is to glide of straight dislocations in the slip direction, and the model corresponds physically to the ladder-like structure of persistent slip bands. 相似文献