全文获取类型
收费全文 | 601840篇 |
免费 | 7197篇 |
国内免费 | 1972篇 |
专业分类
电工技术 | 11362篇 |
综合类 | 625篇 |
化学工业 | 88520篇 |
金属工艺 | 23878篇 |
机械仪表 | 19512篇 |
建筑科学 | 13379篇 |
矿业工程 | 2980篇 |
能源动力 | 16282篇 |
轻工业 | 45983篇 |
水利工程 | 6187篇 |
石油天然气 | 10602篇 |
武器工业 | 80篇 |
无线电 | 74611篇 |
一般工业技术 | 119498篇 |
冶金工业 | 112724篇 |
原子能技术 | 12854篇 |
自动化技术 | 51932篇 |
出版年
2021年 | 5301篇 |
2020年 | 4024篇 |
2019年 | 5142篇 |
2018年 | 8777篇 |
2017年 | 8855篇 |
2016年 | 9420篇 |
2015年 | 5992篇 |
2014年 | 9935篇 |
2013年 | 28414篇 |
2012年 | 15970篇 |
2011年 | 21698篇 |
2010年 | 17273篇 |
2009年 | 19502篇 |
2008年 | 20318篇 |
2007年 | 20072篇 |
2006年 | 18072篇 |
2005年 | 16209篇 |
2004年 | 15496篇 |
2003年 | 15408篇 |
2002年 | 14581篇 |
2001年 | 14444篇 |
2000年 | 13703篇 |
1999年 | 14284篇 |
1998年 | 35389篇 |
1997年 | 24673篇 |
1996年 | 19209篇 |
1995年 | 14504篇 |
1994年 | 12825篇 |
1993年 | 12807篇 |
1992年 | 9572篇 |
1991年 | 8992篇 |
1990年 | 8811篇 |
1989年 | 8299篇 |
1988年 | 7961篇 |
1987年 | 7020篇 |
1986年 | 6849篇 |
1985年 | 7771篇 |
1984年 | 7162篇 |
1983年 | 6438篇 |
1982年 | 5995篇 |
1981年 | 6159篇 |
1980年 | 5731篇 |
1979年 | 5545篇 |
1978年 | 5395篇 |
1977年 | 6250篇 |
1976年 | 7895篇 |
1975年 | 4794篇 |
1974年 | 4616篇 |
1973年 | 4673篇 |
1972年 | 3818篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
991.
T Ohnishi T Yano S Nakano S Jinnouchi S Nagamachi LI Flores H Nakahara K Watanabe 《Canadian Metallurgical Quarterly》1997,38(9):1463-1467
We compared the acetazolamide challenge test using 99mTc-ECD SPECT and 123I-IMP SPECT images in patients with chronic occlusive cerebrovascular disease. We also evaluated the usefulness of linearization correction for acetazolamide challenge test of 99mTc-ECD SPECT. METHODS: Twenty patients with unilateral chronic occlusive cerebrovascular disease (10 patients had middle cerebral arterial lesion and 10 had internal carotid lesion) were included in the study. Split-dose (a dose fractioning was 1:2), and sequential SPECT technique was used for 99mTc-ECD SPECT studies while only acetazolamide challenge test studies for 123I-IMP SPECT were performed. Permeability surface area product model (PS model) and back-diffusion model (Lassen's correction) were used for linearization correction of acetazolamide challenge with 99mTc-ECD SPECT. RESULTS: Six of 16 patients with reduced vasodilatory capacity in 123I-IMP SPECT were underestimated by 99mTc-ECD SPECT acetazolamide challenge test. Relative ECD uptake normalized by cerebellar uptake compared with IMP uptake showed a nonlinear relationship, indicating relatively less uptake in high flow range. The underestimations of limited vasodilatory capacity observed in 99mTc-ECD SPECT without linearization correction was modified by linearization algorithm. However, the effect of correction based on PS model was superior than that of Lassen's correction. The corrected 99mTc-ECD uptake ratio, based on PS model, and IMP uptake ratio demonstrated a better linear relationship than that of Lassen's correction. CONCLUSION: Technetium-99m ECD SPECT corrected based on the PS model is a better method of linearization for evaluating cerebrovascular reserve using acetazolamide challenge. 相似文献
992.
K Fukushima S Hara-Kuge T Ohkura A Seko H Ideo T Inazu K Yamashita 《Canadian Metallurgical Quarterly》1997,272(16):10579-10584
We found that 35S-labeled recombinant human interleukin-1beta (rhIL-1beta) binds phosphatidylinositol-specific phospholipase C-treated human placental alkaline phosphatase, phosphatidylinositol-specific phospholipase C-treated trypanosome surface variant glycoproteins, and urinary uromodulin immobilized on plates or immobilized on CNBr-activated Sepharose 4B. The interaction between rhIL-1beta and these glycoproteins was lectin-like, since it was inhibited in the presence of specific saccharides, i.e. mannose 6-phosphate or synthetic Ac-NH.CH2.CH2. PO4--->6Manalpha1-->(+/-2Manalpha1-->+/-6Manalpha1-->) propyl at about 1 microM. On the other hand, a wide variety of compounds including biantennary sugar chains derived from these glycoproteins as well as ethanolamine phosphate, inositol phosphate, mannose 6-sulfate, mannose 1-phosphate, glucose 6-phosphate, and mannitol 6-phosphate did not show any inhibitory effect at concentrations up to 1 mM. These results indicate that rhIL-1beta interacts with these glycoproteins via the mannose 6-phosphate diester of glycans on the glycosylphosphatidylinositol (GPI) anchor. Furthermore, when monolayers of polarized Madin-Darby canine kidney cells on polycarbonate filter membranes were incubated with 35S-rhIL-1beta in either the apical or basolateral chamber, 35S-interleukin-1beta was found to bind specifically to the apical membranes with a Ka value of 4.6 x 10(7) M-1, and the specific interaction was inhibited by 1 microM mannose 6-phosphate. Since the mannose 6-phosphate diester moiety exists only in the GPI glycans on plasma membranes, it was evident that interleukin-1beta can directly interact with the mannose 6-phosphate diester component of the intact glycan of GPI anchors on plasma membranes. 相似文献
993.
994.
R Middendorff D Müller S Wichers AF Holstein MS Davidoff 《Canadian Metallurgical Quarterly》1997,82(12):4154-4161
Previous studies have demonstrated that nitric oxide (NO) influences Leydig cell function. Here we provide evidence for NO production and activity in seminiferous tubules and blood vessels of the human testis. By immunohistochemistry, the soluble guanylyl cyclase (sGC), the intracellular NO receptor, and the second messenger, cyclic guanosine monophosphate (cGMP), were detected in myofibroblasts of the peritubular lamina propria in Sertoli cells, as well as in endothelial and smooth muscle cells of testicular blood vessels. Performed with isolated tubules and blood vessels, the biological activity of sGC could be proved by cGMP generation in response to treatments with the NO donor, sodium nitroprusside. The endothelial and neuronal subtypes of NO synthase (NOS) were localized immunohistochemically to the same cell types that express sGC and cGMP. In isolated tubules and vessels, the presence of endothelial NOS and neuronal NOS was confirmed by immunoblotting, and NOS activity was demonstrated by decreased cGMP production upon incubation with the NOS inhibitor L-nitro arginine methylester. These findings show that peritubular cells, Sertoli cells, and testicular blood vessels may be sites of NO production and activity, possibly involved in relaxation of seminiferous tubules and blood vessels to modulate sperm transport and testicular blood flow, respectively. 相似文献
995.
Amines such as dopamine, norepinephrine and epinephrine were analysed in the brain regions of O.mossambicus exposed to quinalphos, phenthoate and their combination for 96 hr. The three types of treatments significantly (P < 0.05) altered the amines level at various intervals in the brain regions. 相似文献
996.
S Benk? S Drabant G Grézal I Urm?s M Cs?rg? I Klebovich 《Canadian Metallurgical Quarterly》1997,47(8):913-916
A comparative pharmacokinetic study has been performed in 19 healthy male volunteers in a single-dose, randomized, two way cross-over design with two preparations of gemfibrozil (CAS 25812-30-0) capsules each of them containing 300 mg active ingredient. The test preparation was Innogem 300 mg capsule. The plasma concentration of gemfibrozil was determined by a validated HPLC-UV analytical method. The statistical comparison of individual pharmacokinetic parameters (AUC0-16, AUC0-oc Cmax, tmax) of the two capsule preparations was performed by three-way analysis of variance (ANOVA), Wilcoxon's, Westlake's, Schuirmann's and Hanck-Anderson's method as well as by the calculation of confidence intervals on the ratio of test/reference. The relative bioavailability of the test preparation with respect to the reference preparation in terms of the AUC0-oc was 104.06 +/- 21.61%. No statistically significant difference was found between the pharmacokinetic parameters, calculated from plasma concentration-time curves, indicating that the two preparations were bioequivalent. 相似文献
997.
This study presents a case of vaginoperineal histologically verified endometriosis at the site of episiotomy scar in a 40-year female subject, 17 years after delivery. Apart from episiotomy during delivery manual revision of the uterus was performed and the cervical rupture managed. Residue symptoms occurs 8 months after the first surgical excision. Clinical data indicate that decidua implantation at the site of episiotomy occurred during the manual revision of the uterine cavity during delivery. 相似文献
998.
D Popovi? 《Canadian Metallurgical Quarterly》1997,50(11-12):559-563
Tissue and organ transplantation is a very complex interdisciplinary treatment, particularly in regard to unpaired organs, and it carries numerous risks for all participants in such an action. For the purpose of minimizing the risks to the allowed level and the preservation the humanitarian goals in medicine when performing the transplantation, professional and scientific doctrines and the respect of ethical and legal principles should be strictly observed. The paper presents the basic approaches in the estimation of justification, usefulness and certain forms of responsibility in the process of transplantation. Ethical and legal postulates which support transplantation to prevent deviation, deprivation or delinquency have also been reviewed. 相似文献
999.
1000.
D Brown S Kogan E Lagasse I Weissman M Alcalay PG Pelicci S Atwater JM Bishop 《Canadian Metallurgical Quarterly》1997,94(6):2551-2556
The malignant cells of acute promyelocytic leukemia (APL) contain a reciprocal chromosomal translocation that fuses the promyelocytic leukemia gene (PML) with the retinoic acid receptor alpha gene (RAR alpha). To test the hypothesis that the chimera PMLRAR alpha plays a role in leukemogenesis, we expressed a PMLRAR alpha cDNA in myeloid cells of transgenic mice. PMLRAR alpha transgenic mice exhibited impaired neutrophil maturation early in life, which progressed at a low frequency over the course of several months to overt APL. Both the preleukemic state and the leukemia could be transplanted to nontransgenic mice, and the transplanted preleukemia could progress to APL. The APL recapitulated features of the human disease, including a response to retinoic acid. Retinoic acid caused the leukemic cells to differentiate in vitro and in vivo, eliciting remissions of both the preleukemic state and APL in mice. Our results demonstrate that PMLRAR alpha impairs neutrophil differentiation and initiates the development of APL. The transgenic mice described here provide an apparently accurate model for human APL that includes clear evidence of tumor progression. The model should be useful for exploring the molecular pathogenesis of APL and the mechanisms of the therapeutic response to retinoic acid, as well as for preclinical studies of therapeutic regimens. 相似文献