全文获取类型
收费全文 | 2025篇 |
免费 | 32篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 1篇 |
综合类 | 4篇 |
化学工业 | 18篇 |
金属工艺 | 12篇 |
机械仪表 | 6篇 |
建筑科学 | 3篇 |
矿业工程 | 2篇 |
能源动力 | 4篇 |
轻工业 | 16篇 |
水利工程 | 25篇 |
无线电 | 18篇 |
一般工业技术 | 25篇 |
冶金工业 | 1885篇 |
原子能技术 | 3篇 |
自动化技术 | 39篇 |
出版年
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 6篇 |
2019年 | 2篇 |
2018年 | 10篇 |
2017年 | 1篇 |
2016年 | 5篇 |
2015年 | 6篇 |
2014年 | 10篇 |
2013年 | 17篇 |
2012年 | 3篇 |
2011年 | 4篇 |
2010年 | 6篇 |
2009年 | 2篇 |
2008年 | 2篇 |
2007年 | 4篇 |
2006年 | 4篇 |
2005年 | 18篇 |
2004年 | 5篇 |
2003年 | 10篇 |
2002年 | 16篇 |
2001年 | 10篇 |
2000年 | 2篇 |
1999年 | 59篇 |
1998年 | 617篇 |
1997年 | 375篇 |
1996年 | 220篇 |
1995年 | 109篇 |
1994年 | 90篇 |
1993年 | 99篇 |
1992年 | 15篇 |
1991年 | 23篇 |
1990年 | 16篇 |
1989年 | 25篇 |
1988年 | 30篇 |
1987年 | 19篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 15篇 |
1978年 | 2篇 |
1977年 | 44篇 |
1976年 | 99篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1955年 | 4篇 |
排序方式: 共有2061条查询结果,搜索用时 31 毫秒
51.
BACKGROUND: Ultrasonically activated shears (UAS) have been documented to be both safe and fast devices in laparoscopic surgery. We studied whether the use of UAS would have some advantage in thyroid surgery. METHODS: Thyroidectomies, performed by one senior endocrine surgeon between December 1996 and February 1997, were retrospectively matched, with patients operated on by the same surgeon using the conventional method. RESULTS: Six pairs of total thyroidectomies and one pair of lobectomies could be matched. Mean operating time was 100 minutes for the patients operated on with the UAS and 154 minutes for the patients operated on with the conventional method. The mean operating time with the UAS was thus on average 64.6% of the operation time with the conventional method, with a 95% confidence interval from 50.1% to 83.5% (t = 4.00, 6 df, P = 0.007). CONCLUSIONS: In this material the use of UAS reduced significantly operating time in thyroidectomies. 相似文献
52.
MR Kirshenbaum SF Chen CH Behrens LM Papp MM Stafford JH Sun DL Behrens JR Fredericks ST Polkus P Sipple 《Canadian Metallurgical Quarterly》1994,54(8):2199-2206
(R,R)-2,2'-[1,2-ethanediylbis[imino(1-methyl-2,1-ethanediyl)]]- bis[5-nitro-1H-benz[de]isoquinoline-1,3-(2H)-dione] dimethanesulfonate (DMP 840), is a bis-naphthalimide anticancer tumoricidal agent currently in phase I clinical trials. DMP 840 exhibits curative activity in human tumor xenografts, where it shows selectivity for human solid tumors over murine leukemias. In contrast to the selectivity found for DMP 840 in vivo, DMP 840 exhibits potent antiproliferative activity in vitro against a variety of human and murine leukemia and solid tumor cell lines in culture, with inhibitory doses that reduce the number of treated cells to one half (IC50) values ranging from 2.3 to 53 nM. DMP 840 was growth inhibitory to three doxorubicin-resistant cell lines with IC50 values also in the nanomolar range. Clonogenic survival experiments showed that DMP 840 was equally cytotoxic to both exponentially growing and quiescent human clone A colon carcinoma cells. A 1-h incubation of DMP 840 (1.22-12 microM) caused 5-log cell kill in KB-3-1 human epidermoid carcinoma, clone A human colon carcinoma, and L1210 murine leukemia cell lines. The rapid cell killing by DMP 840 in clonogenic survival experiments and initial mechanism of action studies was consistent with a DNA-interactive mechanism for DMP 840 cytotoxicity. Mechanism of action studies in L1210 leukemia cells demonstrated that DMP 840 inhibited the incorporation of thymidine and uridine into DNA and RNA with IC50 values of 0.55 and 0.08 microM, respectively. DMP 840 produced DNA single-strand breaks in a dose-dependent manner. Double-strand breaks were not observed with DMP 840 treatment, even at higher concentrations of compound. Chinese hamster ovary (CHO) and P388 cells resistant to camptothecin and containing a mutant form of topoisomerase I were also used to evaluate whether DMP 840 was cross-resistant with agents active against topoisomerase I. While the CHOR line was 163-fold resistant to camptothecin, the CHOR line was only 1.7-fold resistant to DMP 840. In summary, DMP 840 is a DNA-interactive agent that demonstrates excellent antiproliferative activity in vitro against cultured tumor cells from both human and murine sources. Its mechanism of tumoricidal activity may be novel. 相似文献
53.
54.
液态金属快速结晶的热力学驱动力 总被引:1,自引:0,他引:1
采用超高真空无容器悬浮熔炼技术使液态Fe和Ni的过冷度分别达200和235K,借助量热法测定出其比热各为48.6和40.5J·mol~(-1)·K~(-1).据此精确计算出深过冷Fe和Ni快速结晶的热力学驱动力△G_(LS),并与Turnbull模型和Dubey-Ramachandrarao模型的近似计算结果相比较,发现这两种近似模型在过冷度超过100K时均产生大于1%的偏差.进一步分析发现,△G_(LS)的计算偏差对深过冷液态金属中晶体形核率的影响极大,因此快速凝固研究中应尽可能精确计算△G_(LS). 相似文献
55.
RT Malison LH Price R Berman CH van Dyck GH Pelton L Carpenter G Sanacora MJ Owens CB Nemeroff N Rajeevan RM Baldwin JP Seibyl RB Innis DS Charney 《Canadian Metallurgical Quarterly》1998,44(11):1090-1098
BACKGROUND: Prior research has suggested reductions in the density of serotonin transporter (SERT) binding sites in blood platelets and post-mortem brain tissue of depressed patients. We sought to determine whether patients with unipolar major depression have diminished SERT availability as assessed by both brainstem [123I] beta-CIT SPECT and platelet [3H]paroxetine binding. METHODS: Drug-free depressed and healthy subjects were injected with 211 +/- 22 MBq [123I] beta-CIT and imaged 24 +/- 2 h later under equilibrium conditions. A ratio of specific to nonspecific brain uptake (V3" = (brainstem-occipital)/occipital), a measure proportional to the binding potential (Bmax/Kd), was used for all comparisons. RESULTS: Results showed a statistically significant reduction in brainstem V3" values in depressed as compared to healthy subjects (3.1 +/- .9 vs. 3.8 +/- .8, p = .02). Platelet [3H]paroxetine binding was not altered (Bmax = 2389 +/- 484 vs. 2415 +/- 538 fmol/mg protein, p = .91) and was not significantly correlated with brainstem [123I] beta-CIT binding (r = -0.14, p = .48). CONCLUSIONS: These data are the first to suggest reductions in the density of brain SERT binding sites in living depressed patients. These findings provide further support for a preeminent role for alterations in serotonergic neurons in the pathophysiology of depression. 相似文献
56.
AJ Bogdanove JF Kim Z Wei P Kolchinsky AO Charkowski AK Conlin A Collmer SV Beer 《Canadian Metallurgical Quarterly》1998,95(3):1325-1330
The "disease-specific" (dsp) region next to the hrp gene cluster of Erwinia amylovora is required for pathogenicity but not for elicitation of the hypersensitive reaction. A 6.6-kb apparent operon, dspEF, was found responsible for this phenotype. The operon contains genes dspE and dspF and is positively regulated by hrpL. A BLAST search revealed similarity in the dspE gene to a partial sequence of the avrE locus of Pseudomonas syringae pathovar tomato. The entire avrE locus was sequenced. Homologs of dspE and dspF were found in juxtaposed operons and were designated avrE and avrF. Introduced on a plasmid, the dspEF locus rendered P. syringae pv. glycinea race 4 avirulent on soybean. An E. amylovora dspE mutant, however, elicited a hypersensitive reaction in soybean. The avrE locus in trans restored pathogenicity to dspE strains of E. amylovora, although restored strains were low in virulence. DspE and AvrE are large (198 kDa and 195 kDa) and hydrophilic. DspF and AvrF are small (16 kDa and 14 kDa) and acidic with predicted amphipathic alpha helices in their C termini; they resemble chaperones for virulence factors secreted by type III secretion systems of animal pathogens. 相似文献
57.
PJ Heins KA Karpinia JW Maruniak JE Moorhead CH Gibbs 《Canadian Metallurgical Quarterly》1998,69(7):812-818
Probing pain threshold (PPT) assessments were conducted in the facial and oral sulci of maxillary central incisors and first molars of 10 periodontally healthy adults. All subjects were systemically healthy, free of pain, and reported no current medication usage. A computer-linked electronic probe, modified to deliver steadily increasing forces up to 200 grams, was used to collect the data. The system contained a subject operated "off-switch" which, upon activation, signaled the computer to record the subject's PPT. Assessments of each subject's PPTs were conducted on 3 separate occasions at 7-day intervals. Results indicated that the facial sulci of the incisors were the most pain sensitive. They displayed a mean PPT of 50.9 +/- 26.6 grams. The oral sulci of the incisors exhibited a mean PPT of 76.5 +/- 45.2 grams. Facial and oral sulci of the molars evidenced mean PPT values of 102.6 +/- 52.1 grams and 113.5 +/- 51.3 grams, respectively. These data suggest that sulci associated with incisor teeth are nearly twice as pain sensitive as sulci associated with molar teeth. In addition, facial sulci are significantly more pain sensitive than oral sulci. Data did not indicate a visit effect nor a side-of-mouth effect on PPT values. 相似文献
58.
A. Gorodkov N. B. Dobrova J.-PH. Dubernard G. I. Kiknadze I. A. Gatchetchiladze V. G. Oleinikov N. B. Kuzmina J. L. Barat CH. Baquey 《Journal of materials science. Materials in medicine》1996,7(3):153-160
The presence of twisted helical flow patterns in the cardiac cavities during ventricular filling and ejection was supposed. This work was intended in order to show that the intra-ventricular trabeculation plays the determining role in such a flow formation and to find some analytical approaches for its analysis. The morphometric study of human left-ventricular and aortic corrosion casts and dynamic measurement of the aorta by MRI-technique were performed. The data were analysed by means of the Mathematica program. Two groups of trabecules were identified that refer to the inlet and outlet of the ventricular blood flow. The first group consists of trabecules of the free left-ventricular wall. The second group consists of long trabecules going along the anterior left-ventricular wall and intracavital lines of the papillary muscles. Both are twisted clockwise and converge in the flow direction. Each group of trabecules is oriented towards the mitral or aortic valve orifices, correspondingly. It was concluded that the helical trabecular organization acts as flow directing paddles that change their mutual orientation during the cardiac cycle evolution. The reorientation of the flow takes place due to sequential contraction of the ventricular structures. The formalization of trabecular orientation will allow one to calculate improved models of implantable substitutes and auxiliary devices for cardio-vascular surgery.Sadly deceased. 相似文献
59.
CH Park K Nishimura M Kitano K Matsuda Y Okamoto T Ban 《Canadian Metallurgical Quarterly》1996,111(5):1092-1102
This study investigated the mechanism of right ventricular failure during bypass of the left side of the heart by precisely assessing right ventricular function with use of a conductance catheter. Bypass of the left side of the heart was established with a centrifugal pump in 10 mongrel dogs weighing 11 to 19 kg. Right ventricular function during left heart bypass was evaluated by two parameters that were both derived from measurement of relative change in right ventricular volume by the conductance catheter technique. One parameter was the right ventricular end-systolic pressure-volume relationship as a load-independent index, and the other was the peak right ventricular pressure-right ventricular stroke volume relationship as a "force-velocity relationship." These parameters were measured in both normal and failing hearts while afterload was increased by bilateral intrapulmonary balloon inflation. Moreover, changes in these relationships were observed by varying assist ratios of left heart bypass from 0% to 100%. Failing heart models were induced by normothermic aortic clamping for 20 minutes. The right ventricular end-systolic pressure-volume relationship in normal hearts did not change, irrespective of the assist ratio of left heart bypass, whereas that in failing hearts decreased from 4.25 +/- 1.41 mm Hg/ml without bypass of the left side of the heart to 3.53 +/- 1.30 mm Hg/ml after 100% assist of left heart bypass (p < 0.05). In the peak right ventricular pressure-right ventricular stroke volume relationship, right ventricular stroke volume was almost constant in normal hearts when afterload was increased regardless of the assist ratio of left heart bypass. Moreover, right ventricular stroke volume was maintained at a higher level during bypass of the left side of the heart compared with that without left heart bypass. However, that slope of the relationship in failing hearts was inversely linear and became significantly steeper after 100% assist of bypass of the left side of the heart compared with that without left heart bypass (-0.131 +/- 0.042 versus -0.051 +/- 0.038, p < 0.005). Therefore ++these two slopes of the relationship intersected at a point that was considered the critical point of afterload during bypass of the left side of the heart. In other words, right ventricular stroke volume was decreased by 100% left heart bypass above the critical point of afterload. In conclusion, this study demonstrates not only that bypass of the left side of the heart results in an increase in right ventricular stroke volume in both normal and failing hearts at the physiologic range of afterload, but also that right ventricular function against higher afterload is impaired by 100% assist of bypass of the left side of the heart in failing hearts. 相似文献
60.
C.C.H.Rosen 《计算机教育》2010,(9):94-96
Students at the University of Derby are required to complete a year in industry as part of their Bachelor of Science degrees.This is a daunting prospect for some of them,and they can be reluctant to engage in the process of finding a placement position.As part of a second year module,students seeking placement are paired with students already on placement in a mentee/mentor relationship to support the second year students in their search for an internship.This arrangement helps the mentees by introducing them to potential role models close to their experience,receiving encouragement from peers and the inculcation of belief that it is possible to find a placement.The mentors also benefit from a recognition of how much they have learnt.However,there are difficulties in establishing and managing the scheme which should be recognised.This paper reports our experience over the last three years. 相似文献