全文获取类型
收费全文 | 3801篇 |
免费 | 47篇 |
专业分类
电工技术 | 30篇 |
综合类 | 3篇 |
化学工业 | 284篇 |
金属工艺 | 27篇 |
机械仪表 | 35篇 |
建筑科学 | 81篇 |
矿业工程 | 5篇 |
能源动力 | 30篇 |
轻工业 | 85篇 |
水利工程 | 36篇 |
石油天然气 | 1篇 |
无线电 | 232篇 |
一般工业技术 | 326篇 |
冶金工业 | 2480篇 |
原子能技术 | 22篇 |
自动化技术 | 171篇 |
出版年
2022年 | 18篇 |
2021年 | 27篇 |
2019年 | 14篇 |
2018年 | 22篇 |
2017年 | 16篇 |
2016年 | 21篇 |
2015年 | 23篇 |
2014年 | 27篇 |
2013年 | 56篇 |
2012年 | 45篇 |
2011年 | 72篇 |
2010年 | 50篇 |
2009年 | 53篇 |
2008年 | 72篇 |
2007年 | 67篇 |
2006年 | 63篇 |
2005年 | 43篇 |
2004年 | 59篇 |
2003年 | 54篇 |
2002年 | 39篇 |
2001年 | 42篇 |
2000年 | 52篇 |
1999年 | 117篇 |
1998年 | 847篇 |
1997年 | 468篇 |
1996年 | 306篇 |
1995年 | 170篇 |
1994年 | 145篇 |
1993年 | 153篇 |
1992年 | 31篇 |
1991年 | 39篇 |
1990年 | 32篇 |
1989年 | 39篇 |
1988年 | 23篇 |
1987年 | 34篇 |
1986年 | 35篇 |
1985年 | 32篇 |
1984年 | 24篇 |
1983年 | 22篇 |
1982年 | 14篇 |
1981年 | 24篇 |
1980年 | 33篇 |
1979年 | 14篇 |
1978年 | 17篇 |
1977年 | 53篇 |
1976年 | 110篇 |
1975年 | 17篇 |
1974年 | 11篇 |
1973年 | 9篇 |
1971年 | 13篇 |
排序方式: 共有3848条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Dipl.-Biol. Michael Gommel Claudia Raichle Patrick Müller Frieder Keller 《Ethik in der Medizin》2005,17(1):21-27
Definition of the problem: Ethical reasoning cannot be enforced. Voluntary understanding is a basic condition for the development of ethical competencies and attitudes. The aim of this survey was to investigate whether the presence of those students who attended our seminars compulsorily would have a negative effect upon the quality of the course. Methods and results: The participants of our small-group seminars in medical ethics were asked to complete a questionnaire on teaching aims, seminar atmosphere, moderation and importance of subjects. One hundred and ninety-two voluntary participants (2001/2) and 293 compulsory participants (2002/3) completed the questionnaire and were statistically compared. There was no significant difference between voluntary and compulsory participants in any of the important items. However, there were considerable differences in some items between male and female participants. Conclusion: We were surprised that there was no difference between the two groups. This leads us to hope that our concept of case-based small-group seminars will prove capable of realising our teaching aims for all students. The difference between male and female participants may have important didactic consequences and will be the subject of further studies. 相似文献
5.
6.
An innovative method for modelling biological processes under anaerobic conditions is presented and discussed. The method is based on titrimetric and off-gas measurements. Titrimetric data is recorded as the addition rate of hydroxyl ions or protons that is required to maintain pH in a bioreactor at a constant level. An off-gas analysis arrangement measures, among other things, the transfer rate of carbon dioxide. The integration of these signals results in a continuous signal which is solely related to the biological reactions. When coupled with a mathematical model of the biological reactions, the signal allows a detailed characterisation of these reactions, which would otherwise be difficult to achieve. Two applications of the method to the enhanced biological phosphorus removal processes are presented and discussed to demonstrate the principle and effectiveness of the method. 相似文献
7.
Energy management for commercial servers 总被引:1,自引:0,他引:1
Servers: high-end, multiprocessor systems running commercial workloads, have typically included extensive cooling systems and resided in custom-built rooms for high-power delivery. Recently, as transistor density and demand for computing resources have rapidly increased, even these high-end systems face energy-use constraints. Commercial-server energy management now focuses on conserving power in the memory and microprocessor subsystems. Because their workloads are typically structured as multiple application programs, system-wide approaches are more applicable to multiprocessor environments in commercial servers than techniques that primarily apply to single-application environments, such as those based on compiler optimizations. 相似文献
8.
IMP dehydrogenase (IMPDH) catalyzes the oxidation of IMP to XMP with the concomitant reduction of NAD+; the enzyme is activated by K+. This reaction is the rate-limiting step in de novo guanine nucleotide biosynthesis. In order to identify functionally important residues in IMPDH, including those involved in substrate and K+ binding, we have mutated 11 conserved Asp and Glu residues to Ala in Escherichia coli IMPDH. The values of kcat, Km, and Ki for GMP, XMP, mizoribine 5'-monophosphate (MMP), and beta-methylene-tiazofurin adenine dinucleotide (TAD) were determined. Five of these mutations caused a significant change (>/=10-fold) in one of these parameters. The Asp248 --> Ala mutation caused 100-fold decrease in the value of kcat and a 25-fold increase in the value of Kii for TAD; these observations suggest that Asp248 is in the NAD+ binding site. The Asp338 --> Ala mutation caused a 600-fold decrease in the value of kcat, but only a 5-10-fold increase in the values of Km for IMP and Kis for IMP analogs, suggesting that Asp338 may be involved in acid-base catalysis as well as IMP binding. The remaining three residues, Asp13, Asp50, and Glu469, appear to be involved in K+ activation; these residues may be ligands at one or more K+ binding sites. Interestingly, changes in the values of Ki for MMP correlate with changes in kcat/KmKm of IMPDH, while no such correlation is observed for GMP, XMP, and TAD. This observation indicates that MMP is a transition state analog for the IMPDH reaction. 相似文献
9.
DL Ellies DW Stock G Hatch G Giroux KM Weiss M Ekker 《Canadian Metallurgical Quarterly》1997,45(3):580-590
To understand the relationship between the expression and the genomic organization of the zebrafish dlx genes, we have determined the genomic structure of the dlx2 and dlx4 loci. This led to the identification of the zebrafish dlx1 and dlx6 genes, which are closely linked to dlx2 and dlx4, respectively. Therefore, the inverted convergent configuration of Dlx genes is conserved among vertebrates. Analysis of the expression patterns of dlx1 and dlx6 showed striking similarities to those of dlx2 and dlx4, respectively, the genes to which they are linked. Furthermore, the expression patterns of dlx3 and dlx7, which likely constitute a third pair of convergently transcribed genes, are indistinguishable. Thus, the overlapping expression patterns of linked Dlx genes during embryonic development suggest that they share cis-acting sequences that control their spatiotemporal expression. The evolutionary conservation of the genomic organization and combinatorial expression of Dlx genes in distantly related vertebrates suggest tight control mechanisms that are essential for their function during development. 相似文献
10.
K Peris MT Onorati G Keller F Magrini P Donati L Muscardin H H?fler S Chimenti 《Canadian Metallurgical Quarterly》1997,137(3):356-360
OBJECTIVE: Thoracic injury remains a major source of morbidity and mortality in urban trauma centers. With the advent and increasing expertise in video assisted thoracic surgery, this modality has become an attractive alternative in the management of patients with thoracic injury. This report will review our experience with video assisted thoracic surgery at a level I trauma center and attempt to further delineate the indications for and timing of thoracoscopy in thoracic trauma. METHODS: We identified 16 patients who had undergone video assisted thoracic surgery following chest trauma between July 1991 and June 1994. There were 15 penetrating and one blunt trauma. All 16 patients were initially treated with tube thoracostomy. From 0-20 days post-injury, video assisted thoracic surgery was attempted with either diagnostic or therapeutic intentions. RESULTS: Twelve of the 16 patients (75%) had successful thoracoscopy. Three patients had diaphragmatic injury excluded and nine patients had successful evacuation of clotted hemothoraces. Evacuation of clotted hemothorax up to 7 days post-injury was safe and easily accomplished. Four patients (25%) had unsuccessful thoracoscopy and were converted to standard thoracotomy; failure was attributed to either suboptimal single lung ventilation or severe pleural inflammatory reaction. The only death in the entire group occurred 10 days after a thoracotomy for retained hemothorax. The median post-operative hospital stay following successful video assisted thoracic surgery was 3.5 days. CONCLUSIONS: Video assisted thoracic surgery can be utilized as an effective and safe method for the initial diagnostic evaluation and surgical management of stable patients with penetrating thoracic trauma. 相似文献