全文获取类型
收费全文 | 2364篇 |
免费 | 9篇 |
专业分类
电工技术 | 1篇 |
化学工业 | 37篇 |
金属工艺 | 11篇 |
机械仪表 | 5篇 |
建筑科学 | 4篇 |
能源动力 | 3篇 |
轻工业 | 7篇 |
无线电 | 35篇 |
一般工业技术 | 47篇 |
冶金工业 | 2206篇 |
自动化技术 | 17篇 |
出版年
2023年 | 4篇 |
2021年 | 12篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 12篇 |
2012年 | 8篇 |
2011年 | 5篇 |
2010年 | 8篇 |
2009年 | 9篇 |
2008年 | 3篇 |
2007年 | 10篇 |
2006年 | 4篇 |
2005年 | 6篇 |
2004年 | 4篇 |
2003年 | 9篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 69篇 |
1998年 | 708篇 |
1997年 | 394篇 |
1996年 | 258篇 |
1995年 | 156篇 |
1994年 | 121篇 |
1993年 | 137篇 |
1992年 | 16篇 |
1991年 | 21篇 |
1990年 | 29篇 |
1989年 | 25篇 |
1988年 | 34篇 |
1987年 | 29篇 |
1986年 | 12篇 |
1985年 | 18篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 12篇 |
1980年 | 17篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 38篇 |
1976年 | 99篇 |
1975年 | 5篇 |
1966年 | 2篇 |
1955年 | 2篇 |
排序方式: 共有2373条查询结果,搜索用时 15 毫秒
101.
DF Brown MJ Muirhead PM Travis SR Vire J Weller M Hauer-Jensen 《Canadian Metallurgical Quarterly》1997,80(5):966-972
BACKGROUND: Few reports have been made regarding the long term safety of implantable venous access devices used for the delivery of chemotherapeutic agents. The authors' goals were to determine the frequency of complications in patients receiving chemotherapy with these devices; to determine whether complications were associated with the mode of chemotherapy delivery (push/bolus or infusional regimens); and to evaluate the influence of other risk factors, including home-based versus hospital-based administration. METHODS: A total of 152 oncology patients at the John L. McClellan Memorial Veterans Administration Medical Center in Little Rock, Arkansas (ages 26-81 years; mean age, 62 years), who underwent surgical placement of an Infus-a-Port (Strato, Inc., Beverly, MA) between May 1, 1992 and May 31, 1994, were evaluated retrospectively for postplacement device complications, such as infection, thrombosis, and mechanical failure. RESULTS: Twenty-seven patients experienced 1 complication each: 17 episodes of device-related sepsis, cellulitis, or fever of unknown origin; 8 episodes of thrombosis or catheter occlusion; 1 episode of drug extravasation; and 1 mechanical failure. Patient age, frequency of port accession, mode of chemotherapy delivery, tumor type, and neutropenia were evaluated as risk factors, but none was statistically significant. Complications were more frequent during the first 90 days after implantation, but they continued to occur throughout the observation period. CONCLUSIONS: Complications attributable to an implantable venous access device were infrequent in this patient population. No differences in complications for patients receiving home-based versus hospital-based chemotherapy administration were noted, opening the possibility of significant time and cost savings with home treatment. 相似文献
102.
The role of catecholamines in the distribution of intrarenal blood flow and in single-nephron glomerular filtration rate (SNGFR) was evaluated in anesthetized Wistar rats by the Hanssen technique. Epinephrine (EPI) and norepinephrine (NOR) were infused to produce elevations of 20-30 mmHg in mean arterial pressure. Superficial and juxtamedullary nephron perfusion and filtration were determined by the presence of Prussian blue dye. In the control group, 100% of the nephrons presented a homogeneous pattern of perfusion and filtration. In contrast, a heterogeneous distribution of the dye was found even in the larger arteries (arciform and radial), indicating variable perfusion and filtration in both superficial and juxtamedullary nephrons. The effects of EPI and NOR were also evaluated in the superficial cortex by the micropuncture technique in two additional groups of Munich-Wistar rats. Mean SNGFR was 27% and 54% lower in the EPI- and NOR-treated groups, respectively. No change in mean intraglomerular hydraulic pressure was observed after EPI or NOR infusion in spite of a highly scattered pattern, indicating an important variability in perfusion along the superficial cortex, and/or different sensitivity of the pre- and post-glomerular arterioles. The present data suggest that EPI and NOR may affect intrarenal hemodynamics by modifying perfusion and filtration in both superficial and juxtamedullary glomeruli and not by shifting blood flow from superficial to juxtamedullary nephrons. The heterogeneous pattern of perfusion was a consequence of differential vasoconstriction along the intrarenal arteries, probably due to different density and/or sensitivity of the adrenergic receptor subtypes present in the intrarenal vascular tree. 相似文献
103.
JC Lovejoy SR Smith GA Bray JP DeLany JC Rood D Gouvier M Windhauser DH Ryan R Macchiavelli R Tulley 《Canadian Metallurgical Quarterly》1997,82(3):765-770
OBJECTIVE: To conceptualize, with fine needle aspiration cytology (FNAC), the early cellular events occurring in and around fresh autogenous and allogenic bone grafts during the first 40 postimplantation days. STUDY DESIGN: Forty-eight cases of bone grafts were studied by FNAC at serial intervals of 10, 20, 30 and 40 postimplantation days. Twenty patients were recipients of autogenous grafts, 16 received 0.6N HCI partially decalcified allogenic bone implants, and 4 received combined autogenous and allogenic bone grafts (included in the allograft group). There were eight control cases of closed fracture shaft femur, which were managed conservatively. RESULTS: The initial cellular responses in autogenous grafts, allografts and controls appear to be a part of the nonspecific reparative process followed by a more specific phase, with a steady increase in relative lymphocyte count from the 20th day onwards. Osteogenesis, as judged by osteoblasts and osteoclasts, was also comparable. CONCLUSION: Partially decalcified allografts appear to be a good substitute for autogenous bone grafts in clinical practice when adequate autogenous material is not available. FNAC is a good technique for studying bone graft responses without interfering with graft uptake. It is helpful in the early detection of subclinical infection or any other pathology at the graft site. 相似文献
104.
An Escherichia coli expression system that exploits the bacterial alkaline phosphatase (PhoA) signal sequence to translocate recombinant human epidermal growth factor (hEGF) to the periplasm was used to evaluate how changes in the composition and sequence of amino acids near the PhoA-hEGF junction influence the periplasmic accumulation of recombinant protein. A series of chimeric structural genes was generated by in vitro replacement of hEGF sequence with analogous segments from the EGF-like domain of human heregulin (HRG), significantly altering the electrostatic character of the amino-terminal region of the mature protein. Quantitation of HRG/EGF protein in E. coli periplasmic extracts, by RP-HPLC, showed a fourfold decrease after one of two acidic residues located in the amino-terminal region of the mature hEGF, near the PhoA junction, was replaced. An additional threefold decrease was observed when the second acidic residue was replaced with a positively charged lysine. Further extension of the amino-terminal HRG sequence, beyond the first six residues, resulted in net neutralization of a more distant EGF acidic residue with no additional effect on protein yield. The importance of having a negatively charged group in the amino-terminal region of the mature protein was confirmed when insertion of an aspartic acid near the amino-terminus of two poorly expressed hybrid protein sequences resulted in a five- to eightfold increase in their recovery from the periplasm. This study demonstrates the importance of having negatively charged residues near the fusion junction of recombinant proteins expressed in E. coli using the PhoA signal sequence for protein export. 相似文献
105.
Travis L. Dixon Terry L. Schell Howard Giles & Kristin L. Drogos 《The Journal of communication》2008,58(3):530-549
Although the study of police–civilian relations has recently entered the intergroup communication arena, there are no studies of actual interactions between these social categories. In part to rectify that stark omission and guided by communication accommodation theory, 313 randomly sampled video recordings from police cars on traffic stops in Cincinnati, Ohio were content analyzed. The study revealed 3 key differences as a function of the officers' and drivers' races: (a) Black drivers were more likely to experience extensive policing during the stop; (b) the communication quality of White drivers was, on average, more positive than that of the Black drivers; and (c) officers' communication behavior was more positive when the officer and driver were of the same race. These findings are consistent with public opinion data and their implications for theory are discussed. 相似文献
106.
107.
To investigate the effects of a new nonNMDA antagonist on the trisynaptic pathways in the hippocampus, the author examined kainate(KA)-induced generalized seizures in rats. A novel nonNMDA antagonist, YM90K, showed the blockade of the Schaffer collaterals in 2-deoxyglucose study (2-DG) and that the CA1-2 pyramidal cells of the hippocampus were preserved seven days after the KA injections. On the other hand, the control and MK-801 (NMDA-antagonist) treated rats did not depress the Schaffer collaterals and showed persistent hypermetabolism of glucose in the CA1 pyramidal cell layer, where neurons were not preserved seven days later. 2-DG was useful to reveal the effects of nonNMDA antagonist on the KA-induced generalized seizures. This suggests that YM90K is a potent nonNMDA antagonist and that it has a neuroprotective effect in rats. 相似文献
108.
109.
We introduce and discuss the term “bad lattice points” which can be seen as a counterpart to the method of good lattice points
for Monte Carlo and quasi-Monte Carlo integration. We show several examples of the occurrence of bad lattice points in the
latter fields and perform a computer search for such point sets.
An erratum to this article is available at . 相似文献
110.