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   9190篇
  免费   610篇
  国内免费   12篇
  9812篇
  2023年   24篇
  2022年   99篇
  2021年   165篇
  2020年   99篇
  2019年   122篇
  2018年   182篇
  2017年   160篇
  2016年   294篇
  2015年   421篇
  2014年   563篇
  2013年   610篇
  2012年   716篇
  2011年   676篇
  2010年   382篇
  2009年   385篇
  2008年   544篇
  2007年   533篇
  2006年   495篇
  2005年   456篇
  2004年   438篇
  2003年   366篇
  2002年   333篇
  2001年   241篇
  2000年   219篇
  1999年   167篇
  1998年   71篇
  1997年   58篇
  1996年   53篇
  1995年   66篇
  1994年   39篇
  1993年   35篇
  1992年   93篇
  1991年   67篇
  1990年   69篇
  1989年   60篇
  1988年   61篇
  1987年   43篇
  1986年   37篇
  1985年   42篇
  1984年   50篇
  1983年   22篇
  1982年   27篇
  1981年   17篇
  1980年   13篇
  1979年   32篇
  1978年   26篇
  1974年   19篇
  1973年   16篇
  1972年   16篇
  1969年   11篇
排序方式: 共有9812条查询结果,搜索用时 0 毫秒
121.
BackgroundIn Phase II/III randomized controlled clinical trials for the treatment of acute uncomplicated malaria, pyronaridine–artesunate demonstrated high efficacy and a safety profile consistent with that of comparators, except that asymptomatic, mainly mild-to-moderate transient increases in liver aminotransferases were reported for some patients. Hepatic safety, tolerability, and effectiveness have not been previously assessed under real-world conditions in Africa.Methods and findingsThis single-arm, open-label, cohort event monitoring study was conducted at 6 health centers in Cameroon, Democratic Republic of Congo, Gabon, Ivory Coast, and Republic of Congo between June 2017 and April 2019. The trial protocol as closely as possible resembled real-world clinical practice for the treatment of malaria at the centers. Eligible patients were adults or children of either sex, weighing at least 5 kg, with acute uncomplicated malaria who did not have contraindications for pyronaridine–artesunate treatment as per the summary of product characteristics. Patients received fixed-dose pyronaridine–artesunate once daily for 3 days, dosed by body weight, without regard to food intake. A tablet formulation was used in adults and adolescents and a pediatric granule formulation in children and infants under 20 kg body weight. The primary outcome was the hepatic event incidence, defined as the appearance of the clinical signs and symptoms of hepatotoxicity confirmed by a >2× rise in alanine aminotransferase/aspartate aminotransferase (ALT/AST) versus baseline in patients with baseline ALT/AST >2× the upper limit of normal (ULN). As a secondary outcome, this was assessed in patients with ALT/AST >2× ULN prior to treatment versus a matched cohort of patients with normal baseline ALT/AST. The safety population comprised 7,154 patients, of mean age 13.9 years (standard deviation (SD) 14.6), around half of whom were male (3,569 [49.9%]). Patients experienced 8,560 malaria episodes; 158 occurred in patients with baseline ALT/AST elevations >2×ULN. No protocol-defined hepatic events occurred following pyronaridine–artesunate treatment of malaria patients with or without baseline hepatic dysfunction. Thus, no cohort comparison could be undertaken. Also, as postbaseline clinical chemistry was only performed where clinically indicated, postbaseline ALT/AST levels were not systematically assessed for all patients. Adverse events of any cause occurred in 20.8% (1,490/7,154) of patients, most frequently pyrexia (5.1% [366/7,154]) and vomiting (4.2% [303/7,154]). Adjusting for Plasmodium falciparum reinfection, clinical effectiveness at day 28 was 98.6% ([7,369/7,746] 95% confidence interval (CI) 98.3 to 98.9) in the per-protocol population. There was no indication that comorbidities or malnutrition adversely affected outcomes. The key study limitation was that postbaseline clinical biochemistry was only evaluated when clinically indicated.ConclusionsPyronaridine–artesunate had good tolerability and effectiveness in a representative African population under conditions similar to everyday clinical practice. These findings support pyronaridine–artesunate as an operationally useful addition to the management of acute uncomplicated malaria.Trial registrationClinicalTrials.gov NCT03201770.

Gaston Tona Lutete and co-workers report on safety and effectiveness of the antimalarial drug pyronaridine-artesunate in African countries.  相似文献   
122.
The human health risk of soils contaminated with As, Pb, Cu, and Zn was evaluated based on pseudo-total concentrations of metal(loid)s, the physiologically based extraction test (PBET), and diffusive gradients in thin films (DGT). Non-carcinogenic (NCR) and carcinogenic (CR) risks exceeded the U.S. Environmental Protection Agency criteria under both the residential and non-residential scenarios. Human bioavailable concentrations (PBET) were much lower than pseudo-total concentrations. The Hazardous Index of NCR (HI (NCR)) for the PBET in the studied soils was 67% and 94% less than that for pseudo-total concentration, respectively, under the non-residential and residential scenarios. Similarly, CR for the PBET was also 65% and 93% less for the two soils. The concentration of metal(loid)s accumulated in the DGT resin was highly correlated with the PBET-extractable concentration (R2 > 0.649). Therefore, for both the CR and HI (NCR), the DGT-calculated risk was linearly related to the PBET-calculated risk for the studied soils under both scenarios. The results suggest that DGT uptake and PBET-extracted concentrations are good surrogates for risk estimation and that both J1 and J2 soils require remediation before their use for residential or non-residential purposes.  相似文献   
123.
Wheat ferredoxin was purified from the leaves of common wheat (Triticum aestivum). The absorption spectrum showed maxima at 465, 425, 332, and 278 nm. The absorbance ratio, A425 nm/A278 nm was 0.49, and the millimolar extinction coefficient at 425 nm was 10.8 mM-1. cm-1. The amino acid composition was determined to be Lys5, His2, Arg1, Asp11, Thr5, Ser7, Glu18, Pro5, Gly6, Ala7, Cys5, Val7, Met1, Ile4, Leu7, Tyr4, Phe1, and Trp1. The total number of amino acid residues was 97. The molecular weight was calculated from the amino acid composition to be 10,829, including iron and sulfur atoms. This value was confirmed by other methods, which were based on the contents of non-heme iron and of terminal amino acid. The N-terminal amino acid was alanine, and the C-terminal amino acid sequence was -Glu-Leu-Thr-AlaCOOH. Comparative studies were performed between T. aestivum ferredoxin and ferredoxins isolated from closely related species; these were T. aegilopoides, T. durum, Ae. squarrosa, and Ae. ovata. No significant differences in the properties of these ferredoxins were detected. It was also shown that these ferredoxins are immunologically homologous. It is, therefore, likely that one molecular species of ferredoxin is distributed through two genera of Triticum and Aegilops.  相似文献   
124.
125.
126.
We examined the direct effect of magnesium ion on aldosterone production by adrenal cells using collagenase-dispersed zona-glomerulosa cells in rats. The effects of magnesium on aldosterone production stimulated by angiotensin II or ACTH were also investigated. Both magnesium sulphate (MgSO4) and magnesium chloride (MgCl2) (0 to 2 mM) decreased aldosterone production in a dose-dependent manner. In comparison with magnesium-free medium, 2 mM MgSO4 inhibited aldosterone production by 73% and MgCl2 by 65%. In addition, MgSO4 showed an inhibitory effect on aldosterone production stimulated by angiotensin II (10pM to 10nM), whereas it had no significant effect on aldosterone production due to ACTH stimulation (10pM to 10nM). These data suggest that magnesium has an inhibitory action on aldosterone production in vitro and may be a physiological regulator of aldosterone production.  相似文献   
127.
Crystal structures of enoyl-coenzyme A (CoA) isomerase from Bosea sp. PAMC 26642 (BoECI) and enoyl-CoA hydratase from Hymenobacter sp. PAMC 26628 (HyECH) were determined at 2.35 and 2.70 Å resolution, respectively. BoECI and HyECH are members of the crotonase superfamily and are enzymes known to be involved in fatty acid degradation. Structurally, these enzymes are highly similar except for the orientation of their C-terminal helix domain. Analytical ultracentrifugation was performed to determine the oligomerization states of BoECI and HyECH revealing they exist as trimers in solution. However, their putative ligand-binding sites and active site residue compositions are dissimilar. Comparative sequence and structural analysis revealed that the active site of BoECI had one glutamate residue (Glu135), this site is occupied by an aspartate in some ECIs, and the active sites of HyECH had two highly conserved glutamate residues (Glu118 and Glu138). Moreover, HyECH possesses a salt bridge interaction between Glu98 and Arg152 near the active site. This interaction may allow the catalytic Glu118 residue to have a specific conformation for the ECH enzyme reaction. This salt bridge interaction is highly conserved in known bacterial ECH structures and ECI enzymes do not have this type of interaction. Collectively, our comparative sequential and structural studies have provided useful information to distinguish and classify two similar bacterial crotonase superfamily enzymes.  相似文献   
128.
Melanoma can develop in a congenital melanocytic nevus (CMN). In fact, a large CMN is associated with a high risk of developing melanoma. Although melanomas arising from CMNs are thought to have a pathogenesis distinct from conventional melanomas, no studies have been conducted on the evolution or tumor heterogeneity of CMN melanomas. We applied multi‐region whole‐exome sequencing to investigate the clonal nature of driver events and evolutionary processes in CMNs and melanomas arising from CMNs. In two patients, we observed an independent subclonal evolution in cancerized fields of CMNs and chromosome 8q amplification in both melanomas arising from CMNs. The amplification of MYC, located in chromosome 8q, was correlated with the percentage of tumor cells expressing high levels of MYC protein detected in melanoma cells by immunohistochemistry. Our analysis suggests that each CMN cell may evolve sporadically and that amplification of MYC might be a key event for melanoma development in CMNs.  相似文献   
129.
Biomolecules, especially proteins and nucleic acids, have been widely studied to develop biochips for various applications in scientific fields ranging from bioelectronics to stem cell research. However, restrictions exist due to the inherent characteristics of biomolecules, such as instability and the constraint of granting the functionality to the biochip. Introduction of functional nanomaterials, recently being researched and developed, to biomolecules have been widely researched to develop the nanobiohybrid materials because such materials have the potential to enhance and extend the function of biomolecules on a biochip. The potential for applying nanobiohybrid materials is especially high in the field of bioelectronics. Research in bioelectronics is aimed at realizing electronic functions using the inherent properties of biomolecules. To achieve this, various biomolecules possessing unique properties have been combined with novel nanomaterials to develop bioelectronic devices such as highly sensitive electrochemical‐based bioelectronic sensing platforms, logic gates, and biocomputing systems. In this review, recently reported bioelectronic devices based on nanobiohybrid materials are discussed. The authors believe that this review will suggest innovative and creative directions to develop the next generation of multifunctional bioelectronic devices.  相似文献   
130.
Fetuses exposed to an inflammatory environment are predisposed to long‐term adverse neurological outcomes. However, the mechanism by which intrauterine inflammation (IUI) is responsible for abnormal fetal brain development is not fully understood. The mechanistic target of rapamycin (mTOR) signaling pathway is closely associated with fetal brain development. We hypothesized that mTOR signaling might be involved in fetal brain injury and malformation when fetuses are exposed to the IUI environment. A well‐established IUI model was utilized by intrauterine injection of lipopolysaccharide (LPS) to explore the effect of IUI on mTOR signaling in mouse fetal brains. We found that microglia activation in LPS fetal brains was increased, as demonstrated by elevated Iba‐1 protein level and immunofluorescence density. LPS fetal brains also showed reduced neuronal cell counts, decreased cell proliferation demonstrated by low Ki67‐positive density, and elevated neuron apoptosis evidenced by high expression of cleaved Caspase 3. Furthermore, we found that mTOR signaling in LPS fetal brains was elevated at 2 hr after LPS treatment, declined at 6 hr and showed overall inhibition at 24 hr. In summary, our study revealed that LPS‐induced IUI leads to increased activation of microglia cells, neuronal damage, and dynamic alterations in mTOR signaling in the mouse fetal brain. Our findings indicate that abnormal changes in mTOR signaling may underlie the development of future neurological complications in offspring exposed to prenatal IUI.  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