全文获取类型
收费全文 | 117615篇 |
免费 | 8725篇 |
国内免费 | 4134篇 |
专业分类
电工技术 | 5986篇 |
技术理论 | 11篇 |
综合类 | 6737篇 |
化学工业 | 20944篇 |
金属工艺 | 6287篇 |
机械仪表 | 7077篇 |
建筑科学 | 9384篇 |
矿业工程 | 2930篇 |
能源动力 | 3297篇 |
轻工业 | 6635篇 |
水利工程 | 1935篇 |
石油天然气 | 6843篇 |
武器工业 | 711篇 |
无线电 | 14082篇 |
一般工业技术 | 14992篇 |
冶金工业 | 6071篇 |
原子能技术 | 1228篇 |
自动化技术 | 15324篇 |
出版年
2024年 | 367篇 |
2023年 | 1731篇 |
2022年 | 2855篇 |
2021年 | 4272篇 |
2020年 | 3245篇 |
2019年 | 2756篇 |
2018年 | 3152篇 |
2017年 | 3513篇 |
2016年 | 3186篇 |
2015年 | 4081篇 |
2014年 | 5495篇 |
2013年 | 6939篇 |
2012年 | 7214篇 |
2011年 | 7723篇 |
2010年 | 6751篇 |
2009年 | 6431篇 |
2008年 | 6102篇 |
2007年 | 5956篇 |
2006年 | 6347篇 |
2005年 | 5680篇 |
2004年 | 3837篇 |
2003年 | 3393篇 |
2002年 | 3017篇 |
2001年 | 2738篇 |
2000年 | 3106篇 |
1999年 | 3518篇 |
1998年 | 3130篇 |
1997年 | 2548篇 |
1996年 | 2393篇 |
1995年 | 1967篇 |
1994年 | 1646篇 |
1993年 | 1203篇 |
1992年 | 896篇 |
1991年 | 721篇 |
1990年 | 543篇 |
1989年 | 488篇 |
1988年 | 419篇 |
1987年 | 229篇 |
1986年 | 201篇 |
1985年 | 126篇 |
1984年 | 106篇 |
1983年 | 75篇 |
1982年 | 87篇 |
1981年 | 61篇 |
1980年 | 45篇 |
1979年 | 34篇 |
1978年 | 14篇 |
1977年 | 39篇 |
1976年 | 18篇 |
1975年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
171.
无线局域网安全问题研究 总被引:10,自引:0,他引:10
为了提供相当于有线局域网的数据安全,IEEE802.11定义了有线等价保密(WEP)协议。然而,最近的研究发现WEP存在严重的缺陷。介绍了无线局域网存在的安全隐患,分析了WEP的结构以及WEP协议的缺陷以及可能遭受的攻击,并探讨了改进方案。 相似文献
172.
173.
There is growing evidence that the amino-terminal globular domain of apolipoprotein B (apoB) is essential for lipoprotein particle formation in the hepatic endoplasmic reticulum. To identify the structural requirements for its function in lipoprotein assembly, cysteine (Cys) pairs required to form the seven disulfide bonds within the amino-terminal 21% of apoB were replaced in groups or individually by serine. Substitution of Cys pairs required for formation of disulfide bonds 1-3 or 4-7 (numbered from amino to carboxyl terminus) completely blocked the secretion of apoB28 in transfected HepG2 cells. To identify the specific disulfide bonds required for secretion, Cys pairs were mutated individually. Substitution of Cys pairs required for disulfide bonds 1, 3, 5, 6, or 7 had little or no impact on apoB28 secretion or buoyant density. In contrast, individual substitution of Cys pair 2 (amino acid residues 51 and 70) or 4 (218 and 234) severely inhibited apoB28 secretion and its capacity to undergo intracellular assembly with lipid. The same assembly and secretion defects were observed when these mutations were expressed as part of apoB50. These studies provide direct evidence that the ability of the internal lipophilic regions of apoB to engage in the recruitment and sequestration of lipid during translation is critically dependent upon a structural configuration contained within or affected by the amino-terminal 5% of the protein. 相似文献
174.
通过密度测定和DSC热分析,观测了超高分子量聚乙烯的辐射效应。实验结果表明:在吸收剂量0—1.13MGy范围内,密度随吸收剂量的增加而增大,熔化热和熔点也有所增加,特别是在低剂量范围内增加十分明显。以上结果都说明,超高分子量聚乙烯在辐照过程中,结晶在完善或有新的结晶形成 相似文献
175.
NF Saba JD Sweeney LC Penn JC Lawton RL Yankee CH Huang MS Schanfield 《Canadian Metallurgical Quarterly》1997,37(3):321-324
PURPOSE: We report a case of postoperative reparalysis in the recovery room, following nebulized epinephrine. The patient was pharmacologically reversed with edrophonium after paralysis with rocuronium. CLINICAL FINDINGS: A 12-yr-old girl developed postoperative reparalysis following the intraoperative administration of rocuronium. A total of 0.92 mg.kg-1 rocuronium was administered. After surgery, pharmacological reversal was achieved with 20 mg edrophonium with 0.15 mg atropine sulfate iv 35 min after the last administration of rocuronium. Muscular relaxation was monitored using an ulnar peripheral nerve stimulator (PNS). After reversal, a full train-of-four and sustained tetanus at 50 Hz were present. In the recovery room, following nebulized epinephrine, the patient became apneic. The patient was paralyzed and an ulnar PNS demonstrated only one faint twitch. The paralysis was reversed with 1.5 mg neostigmine with 0.3 mg glycopyrrolate. CONCLUSION: Postoperative reparalysis following rocuronium may be a cause of postoperative respiratory distress. The definitive diagnosis is made using PNS and observing the response to pharmacological reversal. Nebulized epinephrine may have a previously undescribed role in the development of postoperative reparalysis. 相似文献
176.
C Diamond ML Huang DH Kedes C Speck GW Rankin D Ganem RW Coombs TM Rose JN Krieger L Corey 《Canadian Metallurgical Quarterly》1997,176(3):775-777
The prevalence of human herpesvirus 8 (HHV-8)/Kaposi's sarcoma (KS)-associated herpesvirus was investigated in the semen of 99 human immunodeficiency virus (HIV)-infected men (median CD4 cell count, 357/mm3) by use of a polymerase chain reaction (PCR) assay capable of detecting <10 copies of HHV-8 DNA. Of the subjects, 95 (96%) self-identified as men who have sex with men (MSM), and 3 had a history of clinical KS. Seminal cell specimens were negative for HHV-8 in 98 subjects. None of the 26 without KS (27.1% of 96 tested) who were seropositive for HHV-8 by IFA for latency-associated nuclear antigens had HHV-8 detected in their semen. The only subject with any evidence for seminal HHV-8 DNA was seropositive for HHV-8 and had active KS. HHV-8 was detected in 10 (10.4%) of 96 peripheral blood mononuclear cell specimens. The prevalence of HHV-8 DNA by PCR in semen of HIV-infected MSM without KS is low. 相似文献
177.
本文分析并推导了应力波在弹性体中传播时,质点的运动速度、压力、位移及应力载波的聚流的形成与表达式.利用得到的公式描述了冲击能传感器的工作机理.给出了某风动工具的测试结果. 相似文献
178.
数模混合仿真中模拟信号的恢复及其误差对整个仿真过程具有重要影响。本文探讨了用零阶保持和一阶保持进行信号恢复的方法,比较了它们的误差及工作特点。特别指出了一阶保持中,由于存在积分器复原时间及数字机操作时间的影响而会带来附加的误差,因此一阶保持方法较难达到其理论的精度。 相似文献
179.
SiC(w)/TZP+mullite陶瓷复合材料界面和组成设计与力学性能 总被引:2,自引:1,他引:1
本文从理论上分析了SiC(w)TZP+mullite(p)复合材料界面残余热应力及其在基质内的分布规律。提出在SiC(w)表面涂复Al2O3和在PZT中加入mullite(p)联合作用来降低晶须/基质界面残余热应力的界面设计方案,导出SiC(w)和mullite(p)协同补强PZT的匹配条件。制备了SiC(w)/TZP+mullite(p)复合材料并了SiC(w)表面涂层Al2O3厚度和SiC(w 相似文献
180.