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   806篇
  免费   26篇
  国内免费   4篇
化学   681篇
晶体学   7篇
力学   1篇
数学   60篇
物理学   87篇
  2024年   1篇
  2023年   9篇
  2022年   56篇
  2021年   95篇
  2020年   35篇
  2019年   27篇
  2018年   28篇
  2017年   29篇
  2016年   36篇
  2015年   30篇
  2014年   36篇
  2013年   61篇
  2012年   43篇
  2011年   63篇
  2010年   25篇
  2009年   39篇
  2008年   46篇
  2007年   37篇
  2006年   30篇
  2005年   27篇
  2004年   20篇
  2003年   7篇
  2002年   8篇
  2001年   4篇
  2000年   3篇
  1999年   3篇
  1998年   1篇
  1997年   2篇
  1996年   4篇
  1995年   1篇
  1993年   1篇
  1991年   6篇
  1990年   1篇
  1989年   2篇
  1987年   1篇
  1985年   1篇
  1984年   2篇
  1982年   3篇
  1981年   3篇
  1978年   2篇
  1977年   2篇
  1976年   2篇
  1975年   1篇
  1973年   1篇
  1966年   1篇
  1963年   1篇
排序方式: 共有836条查询结果,搜索用时 31 毫秒
51.
Respiratory syncytial virus infection (RSVI) is an acute medical and social problem in many countries globally. Infection is most dangerous for infants under one year old and the elderly. Despite its epidemiological relevance, only two drugs are registered for clinical use against RSVI: ribavirin (approved in a limited number of countries due to side effects) and palivizumab (Synagis), which is intended only for the prevention, but not the treatment, of infection. Currently, various research groups are searching for new drugs against RSV, with three main areas of research: small molecules, polymeric drugs (proteins and peptides), and plant extracts. This review is devoted to currently developed protein and peptide anti-RSV drugs.  相似文献   
52.
Selenium nanoparticles (SeNPs) have attracted great attention in recent years due to their unique properties and potential bioactivities. While the production of SeNPs has been long reported, there is little news about the influence of reaction conditions and clean-up procedure on their physical properties (e.g., shape, size) as well as their antioxidant activity. This study takes up this issue. SeNPs were synthesized by two methods using cysteine and ascorbic acid as selenium reductants. The reactions were performed with and without the use of polyvinyl alcohol as a stabilizer. After the synthesis, SeNPs were cleaned using various procedures. The antioxidant properties of the obtained SeNPs were investigated using DPPH and hydroxyl radical scavenging assays. It was found that their antioxidant activity does not always depend only on the nanoparticles size but also on their homogeneity. Moreover, the size and morphology of selenium nanoparticles are controlled by the clean-up step.  相似文献   
53.
Two photosensitizing systems: (1) tetrakis(4-hydroxyphenyl)porphyrin (p-THPP) encapsulated in sterically stabilized liposomes (SSL) and (2) p-THPP functionalized by covalent attachment of poly(ethylene glycol) (p-THPP–PEG2000) were studied in vitro. The dark and photo cytotoxicity of these systems were evaluated on two cell lines: HCT 116, a human colorectal carcinoma cell line, and DU 145, a prostate cancer cell line and compared with these determined for free p-THPP. It was demonstrated that both encapsulation in liposomes as well as attachment of PEG chain result in pronounced reduction of the dark cytotoxicity of the parent porphyrin. The liposomal formulation showed higher than p-THPP–PEG2000 photocytotoxicity towards both cell lines used in the studies.  相似文献   
54.
Screening for systemic amyloidosis is typically carried out with abdominal fat aspirates with varying reported sensitivities. Fat aspirates are preferred for use in primary screening instead of organ biopsies as they are less invasive and thereby minimize the potential risk of complications. At Odense Amyloidosis Center, we performed a prospective study on whether the combined use of fat aspirate and tru-cut skin biopsy could increase the diagnostic sensitivity. Both fat aspirates and skin biopsies were screened with Congo Red staining, and positive biopsies were subsequently subtyped using immunoelectron microscopy and mass spectrometry. Seventy-six patients were included. In total, 24 patients had systemic amyloidosis (11 AL, 12 wtATTR, 1 AA), and 6 patients had localized amyloidosis. Combined fat aspirate and skin biopsy were Congo Red-positive in 15 patients (overall sensitivity (OS) 62.5%). Fat aspirates were positive in 14 patients (OS 58.3%), and the skin biopsy was positive in 5 patients (OS 20.8%). In only one patient did the skin biopsy add extra diagnostic information. The sensitivity differed between AL and ATTR amyloidosis—81.8% and 41.7%, respectively. Using skin biopsy as the only screening method is not recommended.  相似文献   
55.
The purpose of the study was to select an environmentally friendly plant biopesticide to protect seed potatoes against phytopathogens. The scope included the evaluation of the antimicrobial activities of 22 plant water extracts, 22 water-glycol extracts, and 3 subcritical carbon dioxide extracts using the agar diffusion method against 10 potato phytopathogens. For the most effective extracts, minimal inhibitory concentration (MIC), chemical composition analysis by gas chromatography–mass spectrometry and in situ assays on seed potatoes were performed. Garlic water extract was finally selected as the most effective in phytopathogen growth inhibition, both in vitro and in situ, with MIC values ranging between 6.3–25 mg/mL. 5-Hydroxymethylfurfural was determined to be the main component of this extract (33.24%). Garlic water extract was proposed as a potential biopesticide against potato phytopathogens.  相似文献   
56.
A benzo[a]anthraquinone ring system, common to a group of angucycline antibiotics, has been prepared by a unique cascade of reactions. The reaction sequence was initiated by a Suzuki-Miyaura cross-coupling between a bromoquinone and vinyl boronic anhdyride. The reaction product is proposed to undergo a 6π-electron cyclization triggered by reductive activation of the quinone. The reaction process is proposed to be autocatalytic.  相似文献   
57.
We prove a dimension compression estimate for homeomorphic mappings of exponentially integrable distortion via a modulus of continuity result by D. Herron and P. Koskela [Mappings of finite distortion: gauge dimension of generalized quasicircles, Illinois J. Math., 2003, 47(4), 1243–1259]. The essential sharpness of our estimate is demonstrated by an example.  相似文献   
58.
The paper presents the possibility of using Al2O3 antireflection coatings deposited by atomic layer deposition ALD. The ALD method is based on alternate pulsing of the precursor gases and vapors onto the substrate surface and then chemisorption or surface reaction of the precursors. The reactor is purged with an inert gas between the precursor pulses. The Al2O3 thin film in structure of the finished solar cells can play the role of both antireflection and passivation layer which will simplify the process. For this research 50×50 mm monocrystalline silicon solar cells with one bus bar have been used. The metallic contacts were prepared by screen printing method and Al2O3 antireflection coating by ALD method. Results and their analysis allow to conclude that the Al2O3 antireflection coating deposited by ALD has a significant impact on the optoelectronic properties of the silicon solar cell. For about 80 nm of Al2O3 the best results were obtained in the wavelength range of 400 to 800 nm reducing the reflection to less than 1%. The difference in the solar cells efficiency between with and without antireflection coating was 5.28%. The LBIC scan measurements may indicate a positive influence of the thin film Al2O3 on the bulk passivation of the silicon.  相似文献   
59.
Using the all-optical poling method, we observed the formation of a surface-relief grating (SRG) in an amorphous polymer film containing azo dye molecules in side chain positions. The experiment consists of a seeding-type process. We used a recently described experimental setup that permits a periodic nonlinear pattern to be produced by the index dispersion of glass. The particular configuration permits photoinduced translation diffusion of the azo chromophores to be observed as the origin of the SRG formation. Analyses of the gratings recorded by use of s (TE) and p (TM) polarization of the writing beams are conducted by atomic-force microscopy. The effect is attributed to mass transport from regions of high isomerization activity to regions of lower activity.  相似文献   
60.
Magnetic resonance imaging (MRI) abilities in pre- and postnatal monitoring of cytomegalovirus-related brain lesions from early prenatal period to infancy are described. Objective of our study is to illustrate the gradual evolution of intracranial abnormalities in a single patient through serial pre- and postnatal MRI. It demonstrates the progress of a cerebral cytomegalovirus infection from fetal to postnatal life with the lack of concordance between prenatal ultrasonography and MRI, and proves the great importance of MRI, being in most cases the only tool for early detection and monitoring of this potentially devastating entity. It was shown that the additional postnatal MRI increases the possibilities in the specific characterization of lesions revealed in the fetus brain, which account for a wide spectrum of different sequences and best spatial resolution of postnatal MRI in comparison with the prenatal one.  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