全文获取类型
收费全文 | 21985篇 |
免费 | 1889篇 |
国内免费 | 1497篇 |
专业分类
25371篇 |
出版年
2024年 | 52篇 |
2023年 | 233篇 |
2022年 | 587篇 |
2021年 | 864篇 |
2020年 | 636篇 |
2019年 | 791篇 |
2018年 | 843篇 |
2017年 | 628篇 |
2016年 | 943篇 |
2015年 | 1420篇 |
2014年 | 1658篇 |
2013年 | 1729篇 |
2012年 | 2045篇 |
2011年 | 1953篇 |
2010年 | 1167篇 |
2009年 | 1109篇 |
2008年 | 1288篇 |
2007年 | 1162篇 |
2006年 | 1057篇 |
2005年 | 887篇 |
2004年 | 871篇 |
2003年 | 688篇 |
2002年 | 550篇 |
2001年 | 362篇 |
2000年 | 289篇 |
1999年 | 255篇 |
1998年 | 193篇 |
1997年 | 152篇 |
1996年 | 150篇 |
1995年 | 117篇 |
1994年 | 110篇 |
1993年 | 63篇 |
1992年 | 88篇 |
1991年 | 70篇 |
1990年 | 80篇 |
1989年 | 62篇 |
1988年 | 44篇 |
1987年 | 45篇 |
1986年 | 27篇 |
1985年 | 27篇 |
1984年 | 33篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1967年 | 2篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Almost every cell in the Drosophila pupal wing forms a single, distally pointing cuticular hair. The function of the frizzled (fz) gene is essential for the elaboration of the normal wing hair pattern. In the absence of fz function hairs develop, but they display an abnormal polarity. We have examined the developmental expression of the fi gene at the RNA level via in situ hybridization and at the protein level via Western blotting. We have found that fz is expressed in all regions of the epidermis before, during, and after the fz cold sensitive period. We have also found that fz function is not required for normal fi expression. We have further found that mutations in several other tissue polarity genes do not noticeably alter the expression or the modification state of the Fz protein. © 1994 Wiley-Liss, Inc. 相似文献
992.
Upregulation of cAMP is a new functional signal pathway of Klotho in endothelial cells 总被引:3,自引:0,他引:3
Yang J Matsukawa N Rakugi H Imai M Kida I Nagai M Ohta J Fukuo K Nabeshima Y Ogihara T 《Biochemical and biophysical research communications》2003,301(2):424-429
We measured angiotensin I-converting enzyme (ACE) activity in a human endothelial cell to characterize the intracellular signal pathways of Klotho. COS-1 cells transfected with naked mouse membrane-form klotho plasmid DNA (pCAGGS-klotho) translated proper Klotho protein. This translated Klotho protein was secreted into the culture medium. Furthermore, ACE activity in human umbilical vein endothelial cells (HUVEC) was upregulated when HUVEC were co-cultured with COS-1 cells that were pre-transfected with pCAGGS-klotho. The conditioned medium from COS-1 cells pre-transfected with pCAGGS-klotho also dose-dependently upregulated ACE in HUVEC. In addition, the conditioned medium induced time- and dose-dependent enhancement of cAMP production in HUVEC. Rp-cAMP, an inhibitor of cAMP-dependent protein kinase A (PKA), inhibited the upregulation of ACE by Klotho protein. Our results suggest that mouse membrane-form Klotho protein acts as a humoral factor to increase ACE activity in HUVEC via a cAMP-PKA-dependent pathway. These findings may provide a new insight into the mechanism of Klotho protein. 相似文献
993.
Purpose
We sought to estimate the risks of adverse obstetric outcomes and disease outcomes associated with severe thrombocytopenia in pregnant women with aplastic anemia (AA).Methods
In a retrospective study, we compared demographics, clinical characteristics, laboratory results, and outcomes between severe thrombocytopenia (ST) and non-severe thrombocytopenia (non-ST) groups comprising pregnant women with AA.Results
Of 61 AA patients, 43 (70%) were diagnosed as AA before pregnancy and 18 (30%) were AA during pregnancy. The ST group exhibited lower gestational age at nadir of platelet count (26.0 versus 37.0 weeks, p<0.001) and at delivery (37.3 versus 39.1 weeks, p = 0.008), and a higher rate of bleeding gums (33.8 versus 7.7%, p = 0.015) than the non-ST group. In addition, the ST group exhibited more transfusions during pregnancy (72.7 versus 15.4%, p<0.001) and postpartum period (45.0 versus 2.7%, p<0.001), and more bone marrow transplant after delivery (25.0 versus 0.0%, p<0.001) than the non-ST group. The ST group had a higher odds ratio of composite disease complications (OR, 9.63; 95% CI, 2.82–32.9; p<0.001) and composite obstetric complications (OR, 6.78; 95% CI, 2.11–21.8; p = 0.001) than the non-ST group.Conclusions
Severe thrombocytopenia is more associated with obstetric and disease complications than is non-severe thrombocytopenia in pregnant women with AA. 相似文献994.
Background
To investigate the distribution of intraocular pressure (IOP) and refractive errors according to age group in a representative sample of non-glaucomatous Korean adults.Methods
A total of 7,277 adults (≥19 years) who participated in the Korea National Health and Nutrition Examination Survey (KNHANES) from 2008 to 2011 underwent ophthalmic examination were divided into three groups according to age: the young- (19–39 years), middle- (40–59 years), and old- (≥60 years) age groups. Simple and multiple regression analyses between IOP and various parameters (including the refractive error) were conducted.Results
The mean IOP of the total population was 14.0±0.1 mmHg [young: 13.9±0.1 mmHg; middle: 14.1±0.1 mmHg; old: 13.8±0.2 mmHg (P for trend = 0.085)]. Myopia and high myopia were more prevalent in the young- (70.8% and 16.1%, respectively), compared to the middle- (44.6% and 10.9%) and old- (8.9% and 2.2%) age groups. Univariate analysis in the total population showed that higher IOP was associated with myopic refractive error, the female gender, higher body mass index (BMI), diabetes, hypertension, and hypercholesterolemia (all P<0.05). In the young- and middle-age groups, higher IOP was associated with myopic refractive error, the female gender, higher BMI, hypercholesterolemia and diabetes (all P<0.05). In the old-age group, the association between IOP and refractive error was not significant (P = 0.828). In multiple linear regression analysis, similar significant relationships between the refractive error and IOP were found in the young- and middle-age groups (beta = −0.08 and −0.12; P = 0.002 and <0.001 for young- and middle-age group, respectively), but not in the old-age group (beta = 0.03; P = 0.728), after adjusting for age, gender, BMI, region of habitation, diabetes, hypertension, and hypercholesterolemia.Conclusions
Myopic refractive error was an independent predictor of higher IOP in non- glaucomatous eyes, and the association between refractive error and IOP differed according to age. 相似文献995.
Identification and nearly full-length genome characterization of novel porcine bocaviruses 总被引:3,自引:0,他引:3
The genus bocavirus includes bovine parvovirus (BPV), minute virus of canines (MVC), and a group of human bocaviruses (HBoV1-4). Using sequence-independent single primer amplification (SISPA), a novel bocavirus group was discovered with high prevalence (12.59%) in piglet stool samples. Two nearly full-length genome sequences were obtained, which were approximately 5,100 nucleotides in length. Multiple alignments revealed that they share 28.7-56.8% DNA sequence identity with other members of Parvovirinae. Phylogenetic analyses indicated their closest neighbors were members of the genus bocavirus. The new viruses had a putative non-structural NP1 protein, which was unique to bocaviruses. They were provisionally named porcine bocavirus 1 and 2 (PBoV1, PBoV2). PBoV1 and PBoV2 shared 94.2% nucleotide identity in NS1 gene sequence, suggesting that they represented two different bocavirus species. Two additional samples (6V, 7V) were amplified for 2,407 bp and 2,434 bp products, respectively, including a partial NP1 gene and the complete VP1 gene; Phylogenetic analysis indicated that 6Vand 7V grouped with PBoV1 and PBoV2 in the genus of bocavirus, but were in the separate clusters. Like other parvoviruses, PBoV1, PBoV2, 6Vand 7V also contained a putative secretory phospholipase A(2) (sPLA(2)) motif in the VP1 unique region, with a conserved HDXXY motif in the catalytic center. The conserved motif YXGXF of the Ca(2+)-binding loop of sPLA2 identified in human bocavirus was also found in porcine bocavirus, which differs from the YXGXG motif carried by most other parvoviruses. The observation of PBoV and potentially other new bocavirus genus members may aid in molecular and functional characterization of the genus bocavirus. 相似文献
996.
The aim of the present study was to investigate the effects of di‐ and sesquiterpenoids isolated from the pods of Sindora sumatrana Miq. (Leguminosae) on P‐glycoprotein (P‐gp) function in an adriamycin‐resistant human breast cancer cell line, MCF‐7/ADR. Over‐expression of P‐gp is known to be one of the mechanisms involved in multidrug resistance (MDR), which is a major obstacle in clinical cancer treatment. Among six di‐ and sesquiterpenoids extracted from S. sumatrana, (+)‐7β‐acetoxy‐15,16‐epoxycleroda‐3,13(16),14‐trien‐18‐oic acid ( 1 ) showed a strong P‐gp inhibitory effect, as great as that of verapamil, a representative P‐gp inhibitor. Compound 1 enhanced daunomycin accumulation more than fourfold and significantly decreased daunomycin efflux compared with control, resulting in a decrease in the IC50 value for daunomycin. These results suggest that compound 1 inhibits the functioning of P‐gp and, therefore, can be developed as an MDR‐reversing agent. 相似文献
997.
Background
There have been several methods developed for the prediction of synthetic metabolic pathways leading to the production of desired chemicals. In these approaches, novel pathways were predicted based on chemical structure changes, enzymatic information, and/or reaction mechanisms, but the approaches generating a huge number of predicted results are difficult to be applied to real experiments. Also, some of these methods focus on specific pathways, and thus are limited to expansion to the whole metabolism. 相似文献998.
The L -aspartate family amino acids (AFAAs), L -threonine, L -lysine, L -methionine and L -isoleucine have recently been of much interest due to their wide spectrum of applications including food additives, components of cosmetics and therapeutic agents, and animal feed additives. Among them, L -threonine, L -lysine and L -methionine are three major amino acids produced currently throughout the world. Recent advances in systems metabolic engineering, which combine various high-throughput omics technologies and computational analysis, are now facilitating development of microbial strains efficiently producing AFAAs. Thus, a thorough understanding of the metabolic and regulatory mechanisms of the biosynthesis of these amino acids is urgently needed for designing system-wide metabolic engineering strategies. Here we review the details of AFAA biosynthetic pathways, regulations involved, and export and transport systems, and provide general strategies for successful metabolic engineering along with relevant examples. Finally, perspectives of systems metabolic engineering for developing AFAA overproducers are suggested with selected exemplary studies. 相似文献
999.
Rye Jin KIM Seung Han OH Mi Young NOH Yong Hun JO Seongon KIM In Seok BANG Yong Seok LEE Iksoo KIM Yeon Soo HAN 《Entomological Research》2010,40(4):217-224
Calreticulin (CRT) plays pivotal roles in Ca2+ homeostasis, molecular chaperoning, infection, inflammation and innate immunity. In an attempt to study the involvement of CRT in innate immunity, the full-length cDNA of calreticulin (PxCRT) was cloned from the diamondback moth, Plutella xylostella. It consists of 1674 bp (excluding poly-A tail) with a longest open reading frame (ORF) of 1197 bp encoding 398 amino acids. In silico analysis of PxCRT ORF reveals that it has various repeat motifs and endoplasmic reticulum retention signal found in all the calreticulin proteins. As expected, high amino acid sequence identities were found from other CRTs identified from Bombyx mori (87%), Galleria mellonella (87%), Apis mellifera (74%), Anopheles gambiae (74%), Tribolium castaneum (73%), Culex quinquefasciatus (73%), Rhodnius prolixus (72%), Nasonia vitripennis (71%), Drosophila melanogaster (71%) and Haemaphysalis qinghaiensis (68%). During development, P. xylostella expressed PxCRT predominantly in the pupal stage. In addition, spatial expression pattern analysis indicates that PxCRT was highly expressed in the silk gland. PxCRT mRNA, furthermore, was strongly induced 3 to 6 h after laminarin treatment, suggesting that PxCRT appears to be involved in immune responses and also plays an important role in the silk gland. 相似文献
1000.
Han J Kim N Joo H Kim E Earm YE 《American journal of physiology. Heart and circulatory physiology》2002,283(4):H1545-H1554
The present investigation tested the hypothesis that nitric oxide (NO) potentiates ATP-sensitive K(+) (K(ATP)) channels by protein kinase G (PKG)-dependent phosphorylation in rabbit ventricular myocytes with the use of patch-clamp techniques. Sodium nitroprusside (SNP; 1 mM) potentiated K(ATP) channel activity in cell-attached patches but failed to enhance the channel activity in either inside-out or outside-out patches. The 8-(4-chlorophenylthio)-cGMP Rp isomer (Rp-CPT-cGMP, 100 microM) suppressed the potentiating effect of SNP. 8-(4-Chlorophenylthio)-cGMP (8-pCPT-cGMP, 100 microM) increased K(ATP) channel activity in cell-attached patches. PKG (5 U/microl) added together with ATP and cGMP (100 microM each) directly to the intracellular surface increased the channel activity. Activation of K(ATP) channels was abolished by the replacement of ATP with ATPgammaS. Rp-pCPT-cGMP (100 microM) inhibited the effect of PKG. The heat-inactivated PKG had little effect on the K(ATP) channels. Protein phosphatase 2A (PP2A, 1 U/ml) reversed the PKG-mediated K(ATP) channel activation. With the use of 5 nM okadaic acid (a PP2A inhibitor), PP2A had no effect on the channel activity. These results suggest that the NO-cGMP-PKG pathway contributes to phosphorylation of K(ATP) channels in rabbit ventricular myocytes. 相似文献