全文获取类型
收费全文 | 201241篇 |
免费 | 2643篇 |
国内免费 | 613篇 |
专业分类
电工技术 | 3480篇 |
综合类 | 150篇 |
化学工业 | 29664篇 |
金属工艺 | 8069篇 |
机械仪表 | 6106篇 |
建筑科学 | 4876篇 |
矿业工程 | 1304篇 |
能源动力 | 5182篇 |
轻工业 | 17485篇 |
水利工程 | 2311篇 |
石油天然气 | 4047篇 |
武器工业 | 8篇 |
无线电 | 23158篇 |
一般工业技术 | 40230篇 |
冶金工业 | 37317篇 |
原子能技术 | 5090篇 |
自动化技术 | 16020篇 |
出版年
2021年 | 1775篇 |
2019年 | 1631篇 |
2018年 | 2646篇 |
2017年 | 2714篇 |
2016年 | 2846篇 |
2015年 | 1857篇 |
2014年 | 3157篇 |
2013年 | 9059篇 |
2012年 | 5166篇 |
2011年 | 7157篇 |
2010年 | 5667篇 |
2009年 | 6418篇 |
2008年 | 6511篇 |
2007年 | 6570篇 |
2006年 | 5642篇 |
2005年 | 5271篇 |
2004年 | 5044篇 |
2003年 | 4930篇 |
2002年 | 4562篇 |
2001年 | 4668篇 |
2000年 | 4601篇 |
1999年 | 4741篇 |
1998年 | 11398篇 |
1997年 | 8133篇 |
1996年 | 6419篇 |
1995年 | 4680篇 |
1994年 | 4278篇 |
1993年 | 4080篇 |
1992年 | 3228篇 |
1991年 | 3079篇 |
1990年 | 2875篇 |
1989年 | 2953篇 |
1988年 | 2829篇 |
1987年 | 2398篇 |
1986年 | 2311篇 |
1985年 | 2718篇 |
1984年 | 2507篇 |
1983年 | 2347篇 |
1982年 | 2095篇 |
1981年 | 2203篇 |
1980年 | 2029篇 |
1979年 | 2125篇 |
1978年 | 2122篇 |
1977年 | 2366篇 |
1976年 | 3190篇 |
1975年 | 1833篇 |
1974年 | 1761篇 |
1973年 | 1772篇 |
1972年 | 1443篇 |
1971年 | 1339篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
Prof. Andrea Baier Dr. Anne Kokel Dr. William Horton Ewa Gizińska Dr. Garima Pandey Prof. Ryszard Szyszka Prof. Béla Török Prof. Marianna Török 《ChemMedChem》2021,16(12):1927-1932
A set of novel hydrazone derivatives were synthesized and analyzed for their biological activities. The compounds were tested for their inhibitory effect on the phosphorylating activity of the protein kinase CK2, and their antioxidant activity was also determined in three commonly used assays. The hydrazones were evaluated for their radical scavenging against the DPPH, ABTS and peroxyl radicals. Several compounds have been identified as good antioxidants as well as potent protein kinase CK2 inhibitors. Most hydrazones containing a 4-N(CH3)2 residue or perfluorinated phenyl rings showed high activity in the radical-scavenging assays and possess nanomolar IC50 values in the kinase assays. 相似文献
4.
Paola Leonor Quan Marina Sabat-Bresc Yanru Guo Margarita Martín Gabriel Gastaminza 《International journal of molecular sciences》2021,22(9)
Recent research on mast cell biology has turned its focus on MRGPRX2, a new member of the Mas-related G protein-coupled subfamily of receptors (Mrgprs), originally described in nociceptive neurons of the dorsal root ganglia. MRGPRX2, a member of this group, is present not only in neurons but also in mast cells (MCs), specifically, and potentially in other cells of the immune system, such as basophils and eosinophils. As emerging new functions for this receptor are studied, a variety of both natural and pharmacologic ligands are being uncovered, linked to the ability to induce receptor-mediated MC activation and degranulation. The diversity of these ligands, characterized in their human, mice, or rat homologues, seems to match that of the receptor’s interactions. Natural ligands include host defense peptides, basic molecules, and key neuropeptides such as substance P and vasointestinal peptide (known for their role in the transmission of pain and itch) as well as eosinophil granule-derived proteins. Exogenous ligands include MC secretagogues such as compound 48/80 and mastoparan, a component of bee wasp venom, and several peptidergic drugs, among which are members of the quinolone family, neuromuscular blocking agents, morphine, and vancomycin. These discoveries shed light on its capacity as a multifaceted participant in naturally occurring responses within immunity and neural stimulus perception, as in responses at the center of immune pathology. In host defense, the mice Mrgprb2 has been proven to aid mast cells in the detection of peptidic molecules from bacteria and in the release of peptides with antimicrobial activities and other immune mediators. There are several potential actions described for it in tissue homeostasis and repair. In the realm of pathologic response, there is evidence to suggest that this receptor is also involved in chronic inflammation. Furthermore, MRGPRX2 has been linked to the pathophysiology of non-IgE-mediated immediate hypersensitivity drug reactions. Different studies have shown its possible role in other allergic diseases as well, such as asthma, atopic dermatitis, contact dermatitis, and chronic spontaneous urticaria. In this review, we sought to cover its function in physiologic processes and responses, as well as in allergic and nonallergic immune disease. 相似文献
5.
Chemical engineering systems often involve a functional porous medium, such as in catalyzed reactive flows, fluid purifiers, and chromatographic separations. Ideally, the flow rates throughout the porous medium are uniform, and all portions of the medium contribute efficiently to its function. The permeability is a property of a porous medium that depends on pore geometry and relates flow rate to pressure drop. Additive manufacturing techniques raise the possibilities that permeability can be arbitrarily specified in three dimensions, and that a broader range of permeabilities can be achieved than by traditional manufacturing methods. Using numerical optimization methods, we show that designs with spatially varying permeability can achieve greater flow uniformity than designs with uniform permeability. We consider geometries involving hemispherical regions that distribute flow, as in many glass chromatography columns. By several measures, significant improvements in flow uniformity can be obtained by modifying permeability only near the inlet and outlet. 相似文献
6.
We considered the magnetohydrodynamic (MHD) free convective flow of an incompressible electrically conducting viscous fluid past an infinite vertical permeable porous plate with a uniform transverse magnetic field, heat source and chemical reaction in a rotating frame taking Hall current effects into account. The momentum equations for the fluid flow during absorbent medium are controlled by the Brinkman model. Through the undisturbed state, both the plate and fluid are in a rigid body rotation by the uniform angular velocity perpendicular to an infinite vertical plate. The perpendicular surface is subject to the homogeneous invariable suction at a right angle to it and the heat on the surface varies about a non-zero unvarying average whereas the warmth of complimentary flow is invariable. The systematic solutions of the velocity, temperature, and concentration distributions are acquired systematically by utilizing the perturbation method. The velocity expressions consist of steady-state and fluctuating situations. It is revealed that the steady part of the velocity field has a three-layer characteristic while the oscillatory part of the fluid field exhibits a multi-layer characteristic. The influence of various governing flow parameters on the velocity, temperature, and concentration are analyzed graphically. We also discuss computational results for the skin friction, Nusselt number, and Sherwood number in the tabular forms. 相似文献
7.
8.
Castro Mateus B. Souza Raphael R. N. Junior Agord M. P. Lima Eduardo R. Manera Leandro T. 《Analog Integrated Circuits and Signal Processing》2021,109(3):647-656
Analog Integrated Circuits and Signal Processing - This paper presents the complete design of a phase locked loop-based clock synthesizer for reconfigurable analog-to-digital converters. The... 相似文献
9.
10.
D.V.N. Harish A. Bharatish H.N. Narasimha Murthy B. Anand K.N. Subramanya 《Ceramics International》2021,47(3):3498-3513
Laser ablation of high-temperature ceramic coatings results in thermal residual stresses due to which the coatings fail by cracking and debonding. Hence, the measurement of such residual stresses during laser ablation process holds utmost importance from the view of performance of coatings in extreme conditions. The present research aims at investigating the effect of laser parameters such as laser pulse energy, scanning speed and line spacing on thermal residual stresses induced in tantalum carbide-coated graphite substrates. Residual stresses were measured using micro-Raman spectroscopy and correlated with Raman peak shifts. Transient thermal analysis was performed using COMSOL Multiphysics to model the single ablated track and residual stresses were reported at low, moderate and high pulse energy regimes. The results showed that the initial laser conditions caused higher tensile residual stresses. Moderate pulse energy regime comprised higher compressive residual stresses due to off centre overlapping of the laser pulses. Higher pulse energy (250 μJ), higher scanning speed (1000 mm/s) and moderate line spacing (20 μm) caused accumulation of tensile residual stresses during the final stage of laser ablation. The deviation of experimental residual stresses from COMSOL numerical model was attributed to unaccounted additional stresses induced during thermal spraying process and deformation potentials in the numerical model. 相似文献