首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1972篇
  免费   139篇
  国内免费   1篇
电工技术   23篇
综合类   10篇
化学工业   729篇
金属工艺   33篇
机械仪表   21篇
建筑科学   67篇
矿业工程   7篇
能源动力   50篇
轻工业   229篇
水利工程   18篇
石油天然气   11篇
无线电   98篇
一般工业技术   356篇
冶金工业   224篇
原子能技术   3篇
自动化技术   233篇
  2023年   45篇
  2022年   128篇
  2021年   160篇
  2020年   74篇
  2019年   64篇
  2018年   85篇
  2017年   63篇
  2016年   87篇
  2015年   81篇
  2014年   81篇
  2013年   142篇
  2012年   123篇
  2011年   150篇
  2010年   96篇
  2009年   90篇
  2008年   87篇
  2007年   82篇
  2006年   71篇
  2005年   59篇
  2004年   54篇
  2003年   40篇
  2002年   41篇
  2001年   15篇
  2000年   19篇
  1999年   9篇
  1998年   13篇
  1997年   14篇
  1996年   9篇
  1995年   11篇
  1994年   10篇
  1993年   16篇
  1992年   11篇
  1991年   5篇
  1990年   8篇
  1989年   5篇
  1988年   5篇
  1987年   7篇
  1986年   4篇
  1985年   8篇
  1984年   4篇
  1983年   4篇
  1982年   2篇
  1981年   5篇
  1980年   2篇
  1979年   6篇
  1978年   2篇
  1977年   3篇
  1976年   3篇
  1975年   2篇
  1955年   1篇
排序方式: 共有2112条查询结果,搜索用时 33 毫秒
81.
Mg–Zn–Al layered double hydroxides (LDHs) with varying amounts of zinc were prepared by the coprecipitation method. Solids were analyzed by XRD and N2 physisorption, confirming the formation of pure LDH phase; and the production of mixed oxides with high specific surface areas (182–276 m2 g−1) after calcination. Band gap energy was also determined, presenting the expected decreasing tendency on increasing zinc amounts. These mixed oxides were tested both for the adsorption of 2,4 dichlorophenoxiacetic acid (2,4-d) and for the photocatalytic degradation of 2,4-d and phenol. Nearly total (97%) degradation of initial 1.45 mmol L−1 of 2,4-d, with 1 g calcined LDH per liter, was accomplished in 9 h, while phenol half-life was as short as 3.5 h, with the catalyst with lowest zinc amount (5 wt.%). Langmuir adsorption isotherms are presented. Solids were also characterized by XRD and FTIR analysis after photocatalytic and adsorption activity, to determine the presence of 2,4-d. The versatility of LDH decomposition products in the elimination of different contaminants by different mechanisms puts them forward as a viable alternative for environmental remediation.  相似文献   
82.
The one-pot self-assembly reaction of copper powder, Reineckes salt, acetone and tris(2-aminoethyl)amine (tren) in dmso affords to obtain a heterometallic compound [Cu(trenac)][Cr(NCS)4(NH3)2](NCS) · 6dmso with novel Schiff-base ligand N-(2-{[(1E)-3-amino-1,3-dimethylbutylidene]amino}ethyl)-N-(2-aminoethyl)ethane-1,2-diamine (trenac). The ligand trenac is generated by metal-directed condensation of tren, acetone and ammonia, formed during the synthetic procedure. X-ray structural investigations showed that the complex consists of [Cu(trenac)]2+ cations, anions of the Reineckes salt [Cr(NCS)4(NH3)2]?, uncoordinated thiocyanate groups and dmso molecules, which are held together by electrostatic forces and hydrogen-bonded interactions. The compound was characterized by EPR spectroscopic and magnetic susceptibility measurements.  相似文献   
83.
Lanthanum-containing Y (LaY) zeolites were prepared by ionic exchange from NaY parent zeolite. The LaY zeolites were de-aluminated by steaming. De-aluminated zeolites presented different Si/Al ratio. The physicochemical properties of these catalysts were characterized by X-ray diffraction, pyridine and xenon adsorption, infrared spectroscopy and 29Si, 27Al, 129Xe, 139La solid-state nuclear magnetic resonance spectroscopy. Furthermore, a fractal geometry approach was adopted to describe the evolution in the texture as a consequence of de-alumination. The catalytic properties of materials were evaluated in the n-hexane cracking reaction. The catalyst with the highest catalytic activity was the zeolite highest de-aluminated (Si/Al ratio of 3.7). Such performance was attributed on the one hand, to active extra-framework aluminum species hosted in the large cavities of zeolites and, on the other hand to redistribution of lanthanum species into the zeolite as a consequence of de-alumination.  相似文献   
84.
Obesity is associated with lipid abnormalities leading to an increased morbidity and mortality from atherosclerotic disease. Lipid transfer proteins such as Cholesteryl Ester Transfer Protein (CETP) and Phospholipid Transfer Protein (PLTP), and lipases such as lipoprotein lipase (LPL) and hepatic lipase (HL) are involved in the pathogenesis of the obesity associated proatherogenic dyslipidemia. Nineteen severely obese female subjects undergoing laparosopic gastric banding participated in this prospective study. Subjects were examined with respect to body composition, lipid profile, CETP, PLTP, LPL and HL before and 1 year after surgical treatment. Mean weight loss was 22.2 kg, mainly due to losses in the fat depots. Triglycerides decreased and HDL2-C increased significantly. In respect to transfer proteins mean CETP mass decreased from 1.82 to 1.71 μg mL?1 (P = 0.043) and mean PLTP activity was reduced from 7.15 to 6.12 μmol mL?1 h?1 (P = 0.002), in parallel. In addition, both mean LPL activity and mean HL activity tended to decrease from 297 to 248 nmol mL?1 h?1 for LPL (P = 0.139) and from 371 to 319 nmol mL?1 h?1 for HL (P = 0.170), respectively. We conclude that weight loss induced by bariatric surgery is associated with the amelioration of the obesity-associated dyslipidemic state. This improvement may be attributable to decreased mass and action of the adipocyte tissue derived lipid transfer proteins CETP and PLTP.  相似文献   
85.
An efficient protocol for the rapid room temperature deacetylation of carbohydrate derivatives using CuFe2O4 nanoparticles as an inexpensive and reusable catalyst is presented. After separation of the catalyst with an external magnet, the reaction products are easily obtained in good purity and excellent yields.  相似文献   
86.
Androgen deprivation therapy (ADT) and androgen receptor (AR)-targeted therapy are the gold standard options for treating prostate cancer (PCa). These are initially effective, as localized and the early stage of metastatic disease are androgen- and castration-sensitive. The tumor strongly relies on systemic/circulating androgens for activating AR signaling to stimulate growth and progression. However, after a certain point, the tumor will eventually develop a resistant stage, where ADT and AR antagonists are no longer effective. Mechanistically, it seems that the tumor becomes more aggressive through adaptive responses, relies more on alternative activated pathways, and is less dependent on AR signaling. This includes hyperactivation of PI3K-AKT-mTOR pathway, which is a central signal that regulates cell pro-survival/anti-apoptotic pathways, thus, compensating the blockade of AR signaling. The PI3K-AKT-mTOR pathway is well-documented for its crosstalk between genomic and non-genomic AR signaling, as well as other signaling cascades. Such a reciprocal feedback loop makes it more complicated to target individual factor/signaling for treating PCa. Here, we highlight the role of PI3K-AKT-mTOR signaling as a resistance mechanism for PCa therapy and illustrate the transition of prostate tumor from AR signaling-dependent to PI3K-AKT-mTOR pathway-dependent. Moreover, therapeutic strategies with inhibitors targeting the PI3K-AKT-mTOR signal used in clinic and ongoing clinical trials are discussed.  相似文献   
87.
The interaction of the nucleocapsid NCp7 of the human immunodeficiency virus type 1 (HIV-1) Gag polyprotein with the RNA packaging signal Psi ensures specific encapsidation of the dimeric full length viral genome into nascent virus particles. Being an essential step in the HIV-1 replication cycle, specific genome encapsidation represents a promising target for therapeutic intervention. We previously selected peptides binding to HIV-1 Psi-RNA or stem loops (SL) thereof by phage display. Herein, we describe synthesis of peptide variants of the consensus HWWPWW motif on membrane supports to optimize Psi-RNA binding. The optimized peptide, psi-pepB, was characterized in detail with respect to its conformation and binding properties for the SL3 of the Psi packaging signal by NMR and tryptophan fluorescence quenching. Functional analysis revealed that psi-pepB caused a strong reduction of virus release by infected cells as monitored by reduced transduction efficiencies, capsid p24 antigen levels, and electron microscopy. Thus, this peptide shows antiviral activity and could serve as a lead compound to develop new drugs targeting HIV-1.  相似文献   
88.
The thermal conductivity of insulating polymers can be increased by the addition of conductive fillers. One potential market for these thermally conductive resins is for fuel cell bipolar plates. In this study, various amounts of three different carbon fillers (carbon black, synthetic graphite particles, and carbon fiber) were added to Vectra A950RX liquid crystal polymer. Because the resulting composites were anisotropic, they were tested for both through‐plane and in‐plane thermal conductivities. The effects of single fillers and combinations of the different fillers were studied via a factorial design. Each single filler caused a statistically significant increase in composite through‐plane and in‐plane thermal conductivities at the 95% confidence level, with synthetic graphite causing the largest increase. All of the composites containing combinations of the different fillers caused statistically significant increases in the composite through‐plane and in‐plane thermal conductivities. It is possible that thermally conductive pathways were formed that linked these carbon fillers, which resulted in increased composite thermal conductivity. Composites containing 70, 75, and 80 wt % synthetic graphite and the composite containing all three fillers (2.5 wt % carbon black, 65 wt % synthetic graphite, and 5 wt % carbon fiber) had in‐plane thermal conductivities of 20 W m?1 K?1 or higher, which is desirable for bipolar plates. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   
89.
The influence of lipid peroxidation and heating duration on the amino acid pattern of wheat rolls was assessed in a model baking test. Therefore, three different types of dough were prepared including dough without any fat and two doughs with fat. To estimate the impact of lipid peroxidation products on the amino acid pattern, the two doughs containing fat were both made with rapeseed oil, one with fresh oil, the other with oxidised rapeseed oil. All kinds of dough were baked for three different duration times (18, 24 and 30 min). The lipid peroxidation status of both rapeseed oils was measured with the peroxide value and the p‐anisidine value of the unbaked fat. The amino acid content was analysed by HPLC after acid and alkaline hydrolysis. Besides determining water content and protein content, a sensory analysis was performed. Whereas the amino acid content in the dough without fat was only affected by the baking time, the doughs with rapeseed oil additionally showed a significant increase in amino acid degradation caused by lipid peroxidation products. Especially in the dough prepared with oxidised rapeseed oil, the amino acid content was partly decreased in raw dough without any heating influence. Confirming the influence of lipid peroxidation products in dough prepared with oxidised rapeseed oil, sensory analysis also showed the significantly worst overall score.  相似文献   
90.

Definition of the problem

The central foundations of successful dental treatment consist of a trustful patient-dentist relationship, the professional and psychosocial expertise of the team treating the patient, and consideration of ethical aspects both during the therapeutic decision-making process and during the subsequent execution of therapy. This is especially true of the dental treatment of (mostly elder) persons with dementia, calling for an in-depth assessment of the various normative implications.

Arguments

In geriatric dentistry in particular, situational dilemmas regarding treatment often arise from specific constellations (e.?g. greatly reduced potential for dental therapy, lack of ability regarding oral hygiene and lack of individual patient responsibility) combined with an acute need for treatment and the necessary involvement of third parties. These dilemmas frequently place additional professional and normative demands on the dentist. The current contribution discusses this specific situation, first by way of theoretical discourse and subsequently with a case-related approach on the basis of two case histories.

Conclusion

It becomes clear here that classic state-of-the-art therapies are replaced by “compromise treatment” in many cases in geriatric dentistry. Such treatment follows divergent diagnostic and therapeutic rules, poses changed requirements in terms of communication and presents specific ethical challenges and pitfalls.
  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号