全文获取类型
收费全文 | 310240篇 |
免费 | 3576篇 |
国内免费 | 1913篇 |
专业分类
电工技术 | 6096篇 |
综合类 | 303篇 |
化学工业 | 45511篇 |
金属工艺 | 14051篇 |
机械仪表 | 9473篇 |
建筑科学 | 7729篇 |
矿业工程 | 965篇 |
能源动力 | 7912篇 |
轻工业 | 29566篇 |
水利工程 | 2619篇 |
石油天然气 | 3601篇 |
武器工业 | 44篇 |
无线电 | 37257篇 |
一般工业技术 | 59540篇 |
冶金工业 | 60905篇 |
原子能技术 | 6347篇 |
自动化技术 | 23810篇 |
出版年
2021年 | 2399篇 |
2019年 | 2151篇 |
2018年 | 3792篇 |
2017年 | 3691篇 |
2016年 | 4111篇 |
2015年 | 2797篇 |
2014年 | 4612篇 |
2013年 | 14053篇 |
2012年 | 7587篇 |
2011年 | 10307篇 |
2010年 | 8448篇 |
2009年 | 9342篇 |
2008年 | 9892篇 |
2007年 | 9942篇 |
2006年 | 8974篇 |
2005年 | 8218篇 |
2004年 | 7869篇 |
2003年 | 7819篇 |
2002年 | 7750篇 |
2001年 | 7829篇 |
2000年 | 7265篇 |
1999年 | 7775篇 |
1998年 | 19582篇 |
1997年 | 13756篇 |
1996年 | 10587篇 |
1995年 | 7966篇 |
1994年 | 7028篇 |
1993年 | 6904篇 |
1992年 | 4937篇 |
1991年 | 4933篇 |
1990年 | 4565篇 |
1989年 | 4455篇 |
1988年 | 4283篇 |
1987年 | 3711篇 |
1986年 | 3655篇 |
1985年 | 4251篇 |
1984年 | 3757篇 |
1983年 | 3430篇 |
1982年 | 3147篇 |
1981年 | 3204篇 |
1980年 | 3035篇 |
1979年 | 2859篇 |
1978年 | 2797篇 |
1977年 | 3515篇 |
1976年 | 5019篇 |
1975年 | 2450篇 |
1974年 | 2316篇 |
1973年 | 2281篇 |
1972年 | 1904篇 |
1971年 | 1725篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Serum vanadium, aluminum, silicon and beta 2-microglobulin levels as well as the red cell count, hemoglobin and systolic blood pressure were simultaneously measured in 80 chronic hemodialysis patients. The serum vanadium level was positively correlated with the serum levels of aluminum, silicon and beta 2-microglobulin as well as the systolic blood pressure, and was inversely correlated with the red cell count and hemoglobin. The mean serum vanadium level was 18.4 +/- 7.6 ng/ml before hemodialysis and decreased to 13.0 +/- 5.30 ng/ml at the completion of dialysis. The dialysate vanadium level increased from 0.4 +/- 0.2 (inflow) to 1.0 +/- 0.4 ng/ml (outflow). It was concluded that vanadium was transferred from blood to dialysate when purified water was used in the preparation of the dialysate. 相似文献
72.
LW Seymour H Soyez A De Marre MA Shoaibi EH Schacht 《Canadian Metallurgical Quarterly》1996,11(5):351-365
Prodrugs of mitomycin C (MMC) based on soluble poly-[N-(2-hydroxyethyl)-L-glutamine] (pHEG) polymers have been evaluated as tumour-targeted drugs. These materials are designed to exploit the enhanced permeability of tumour vasculature, combining a passive tumour tropism with decreased systemic liberation of free MMC. A tri- or tetrapeptide linkage (e.g. Gly-Phe-Ala-Leu) between pHEG and the aziridine nitrogen of MMC can combine good hydrolytic stability with rapid cleavage by lysosomal enzymes, releasing free MMC. The conjugates showed decreased systemic toxicity and could be administered to mice at a total MMC dose of 15 mg/kg i.v., compared with just 6 mg/kg for free MMC. Conjugates also showed better activity against animal models of established tumours, achieving up to 77% increased life span (ILS) against solid P388 leukaemia, compared with only 23% for free MMC, and up to 121% ILS against solid C26 colorectal carcinoma, compared with no activity for the free drug. Improving the therapeutic index of anticancer drugs by combining tumour tropism with decreased systemic toxicity is a versatile approach that should produce a new generation of improved anticancer agents. 相似文献
73.
The impact of crosstalk in an arrayed-waveguide N×N wavelength multiplexer is investigated precisely in relation to its application to wavelength-routing N×N all optical networks. In such systems multiple crosstalk light which has the same wavelength as the signal results in signal-crosstalk beat noise. We confirm that the noise is Gaussian and obtain the relation between crosstalk and power penalty. It is shown that the crosstalk must be less than -38 dB for a 16×16 system to keep the power penalty below 1 dB at a bit error rate of 10-9 相似文献
74.
In summary, recent literature indicates that the complications of chronic otitis media have been decreasing. However, even with the advent of modern and more powerful antimicrobials and aggressive surgical eradication of disease, the morbidity and mortality are still high. Some complications may initially be quite obvious and some complications may be quite subtle. Therefore, the most important tools in making early diagnosis are careful history and physical examination, and a high index of suspicion for impending complications. 相似文献
75.
Modeling ion implantation of HgCdTe 总被引:2,自引:0,他引:2
H. G. Robinson D. H. Mao B. L. Williams S. Holander-Gleixner J. E. Yu C. R. Helms 《Journal of Electronic Materials》1996,25(8):1336-1340
Ion implantation of boron is used to create n on p photodiodes in vacancy-doped mercury cadmium telluride (MC.T). The junction
is formed by Hg interstitials from the implant damage region diffusing into the MC.T and annihilating Hg vacancies. The resultant
doping profile is n+/n-/p, where the n+ region is near the surface and roughly coincides with the implant damage, the n- region is where Hg vacancies have been annihilated revealing a residual grown-in donor, and the p region remains doped by
Hg vacancy double acceptors. We have recently developed a new process modeling tool for simulating junction formation in MC.T
by ion implantation. The interstitial source in the damage region is represented by stored interstitials whose distribution
depends on the implant dose. These interstitials are released into the bulk at a constant, user defined rate. Once released,
they diffuse away from the damage region and annihilate any Hg vacancies they encounter. In this paper, we present results
of simulations using this tool and show how it can be used to quantitatively analyze the effects of variations in processing
conditions, including implant dose, annealing temperature, and doping background. 相似文献
76.
D Sternberg A Peled E Shezen O Abramsky W Jiang F Bertolero D Zipori 《Canadian Metallurgical Quarterly》1996,2(1):29-38
The immunological agglutination reactions of physically absorbed F(ab')2 molecules onto anionic and cationic latex particles have been investigated by means of optical absorbance measurements. These measurements have been conducted under different conditions to determine the most influential factors. Surface F(ab')2 and BSA densities, particle concentration in the reaction medium and polyethylene glycol concentration are some of these factors. Sensitized cationic and anionic latexes differ considerably with respect to their colloidal stability and reactivity. As a general rule, the sensitized cationic latex has a relatively higher colloidal stability and hence, it provides reagents with a better optical response. Less than 0.025 microgram/ml of C-reactive protein has been detected using this particle enhanced optical immunoassay. 相似文献
77.
78.
BACKGROUND AND DESIGN: Giant aggressive keratoacanthoma is a rare destructive subset of keratoacanthoma that frequently involves the facial region, grows rapidly to a large size, and often recurs after surgical management. The effectiveness of ionizing radiation therapy was examined in a retrospective study involving 16 patients; 14 of the tumors had recurred after surgical therapy. RESULTS: All tumors resolved with satisfactory cosmetic results and without recurrence following a fractionated course of superficial radiation therapy. CONCLUSIONS: Radiation therapy is an effective therapeutic modality for giant aggressive keratoacanthomas. 相似文献
79.
O. A. Ustrekhova T. G. Ezhikova-Babakhanova G. B. Basov 《Chemistry and Technology of Fuels and Oils》1993,29(11):544-548
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 11, pp. 17–18, 23, November, 1993. 相似文献
80.
N Usui S Kamata S Ishikawa T Sawai H Okuyama K Imura A Okada 《Canadian Metallurgical Quarterly》1996,31(2):258-262
Bone marrow examination revealed a lipid-laden histiocytosis in seven patients undergoing long-term total parenteral nutrition necessitated by extensive short-bowel surgical resection. Clinical abnormalities occurred during this treatment which required bone marrow examination. These included hepatosplenomegaly and peripheral blood cytopenia; the median time to the detection of these abnormalities was 64 months. The most striking change within the bone marrow was the presence of many pigment-laden histiocytes which had the typical morphology of sea-blue histiocytes seen in the so-called idiopathic sea-blue histiocyte syndrome. The occurrence of sea-blue histiocytosis in the bone marrow in association with long-term parenteral nutrition for short-bowel syndrome has not, to our knowledge, been reported previously and should now be considered in the differential diagnosis of bone marrow sea-blue histiocytosis. 相似文献