全文获取类型
收费全文 | 5583篇 |
免费 | 379篇 |
专业分类
5962篇 |
出版年
2023年 | 23篇 |
2022年 | 68篇 |
2021年 | 116篇 |
2020年 | 63篇 |
2019年 | 93篇 |
2018年 | 110篇 |
2017年 | 116篇 |
2016年 | 161篇 |
2015年 | 234篇 |
2014年 | 267篇 |
2013年 | 403篇 |
2012年 | 509篇 |
2011年 | 464篇 |
2010年 | 264篇 |
2009年 | 238篇 |
2008年 | 381篇 |
2007年 | 351篇 |
2006年 | 336篇 |
2005年 | 295篇 |
2004年 | 296篇 |
2003年 | 273篇 |
2002年 | 197篇 |
2001年 | 54篇 |
2000年 | 36篇 |
1999年 | 42篇 |
1998年 | 71篇 |
1997年 | 51篇 |
1996年 | 61篇 |
1995年 | 41篇 |
1994年 | 30篇 |
1993年 | 28篇 |
1992年 | 30篇 |
1991年 | 30篇 |
1990年 | 15篇 |
1989年 | 19篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 13篇 |
1985年 | 17篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1982年 | 22篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1979年 | 14篇 |
1978年 | 10篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1971年 | 4篇 |
1941年 | 4篇 |
排序方式: 共有5962条查询结果,搜索用时 18 毫秒
131.
132.
Claudio Nicolini Andrew S. Belmont Antonietta Martelli 《Cell biochemistry and biophysics》1986,8(2):103-117
Using HeLa S-3 cells synchronized by selective detachment, in this paper we report a parallel study of nuclear morphology
and autoradiography grain patterns between middle G1 and middle S phases: Our results show two distinct [3H]-thymidine labeling patterns. The first “peripheral” labeling pattern has a characteristic nuclear size distribution, in
contrast to the heterogeneous and varying size distributions of Feulgen-stained nuclei, and apparently is characteristic of
very early S phase. The sizes of the second labeling pattern—homogeneous or inhomogeneous grain distribution throughout the
nucleus—are equal or larger than the first and vary with S phase progression. Together, the corresponding nuclear sizes of
the labeled nuclei represent the larger extreme of nuclear areas, and the labeling index closely parallels the fraction of
nuclei with areas larger than the minimum size of the labeled nuclei. These results suggest a characteristic nuclear size
(reflecting unique intranuclear DNA distribution) as a necessary, if not sufficient, requirement for S phase initiation. Parallel
experimentation with rat liver cells—synchronized in vivo by partial hepatectomy and analyzed by thin section autoradiography—confirms
the existence of a peripheral labeling pattern in both the very early part and the very late part of S phase, which reconciles
our data with previous results and points to the fact that both initiation and termination sites for DNA replication are near
the nuclear periphery. 相似文献
133.
Costa-Neto CM Parreiras-E-Silva LT Ruller R Oliveira EB Miranda A Oliveira L Ward RJ 《Biochemical and biophysical research communications》2006,347(3):634-640
The eukaryotic translation initiation factor 5A (eIF5A) is a protein ubiquitously present in archaea and eukarya, which undergoes a unique two-step post-translational modification called hypusination. Several studies have shown that hypusination is essential for a variety of functional roles for eIF5A, including cell proliferation and synthesis of proteins involved in cell cycle control. Up to now neither a totally selective inhibitor of hypusination nor an inhibitor capable of directly binding to eIF5A has been reported in the literature. The discovery of such an inhibitor might be achieved by computer-aided drug design based on the 3D structure of the human eIF5A. In this study, we present a molecular model for the human eIF5A protein based on the crystal structure of the eIF5A from Leishmania brasiliensis, and compare the modeled conformation of the loop bearing the hypusination site with circular dichroism data obtained with a synthetic peptide of this loop. Furthermore, analysis of amino acid variability between different human eIF5A isoforms revealed peculiar structural characteristics that are of functional relevance. 相似文献
134.
Claudio Stasolla Edward C. Yeung 《In vitro cellular & developmental biology. Plant》1999,35(4):316-319
Summary The effects of exogenous applications of ascorbic acid on white spruce somatic embryogenesis were examined. Increasing concentrations
of ascorbate (1 μM to 100 μM) in the germination medium enhanced somatic embryo conversion in a linear fashion. At the optimal ascorbate level (100 μM) the number of embryos able to undergo normal conversion, i.e., emergence of both root and shoot, increased from 34% (control)
to 58%. The effect of ascorbate had a more pronounced effect on shoot growth than on root emergence; and at 100 μM ascorbate, the percentage of embryos able to produce new leaf primordia increased from 47% (control) to 79%. Root emergence
increased slightly from 64% in the control embryos to 74% in the presence of ascorbic acid. The ascorbate-treated embryos
were characterized by an enlarged apical region, presumably due to a larger number of leaf primordia produced, and by dark
green leaves. When allowed to grow further, these embryos were able to develop into normal plantlets. 相似文献
135.
Vismara C Di Muzio A Tarca S Lucchino M Foti I Caloni F 《Birth defects research. Part B, Developmental and reproductive toxicology》2006,77(3):234-237
BACKGROUND: The principal Aflatoxin B(1) (AFB(1)) hydroxylated metabolite excreted in milk is Aflatoxin M(1) (AFM(1)) classified in group 2B by the International Agency for Research on Cancer (IARC). Human exposure to AFM(1) is due to the consumption of contaminated dairy products and partly to endogenous production through AFB(1) liver metabolism. METHODS: Since no data are available on AFM(1) embryotoxicity, its lethal and teratogenic potential was investigated using the Frog Embryo Teratogenesis Assay-Xenopus (FETAX). Stage-8 blastulae were exposed to AFM(1) at 1, 4, 16, 64, and 256 microg/L concentrations until stage 47, free-swimming larva. RESULTS: A slight increase of mortality and malformed larva percents was found in AFM(1)-exposed groups but these differences were not statistically significant in comparison with the controls. CONCLUSIONS: Therefore, AFM(1) is a non-embryotoxic compound when evaluated with a FETAX model at concentrations under the conditions tested. However, AFM(1) merits further studies using mammals as experimental models to identify a possible risk during human pregnancy. 相似文献
136.
Claudio Orizio Renza Perini Arsenio Veicsteinas 《European journal of applied physiology and occupational physiology》1989,58(5):528-533
The contracting muscle generates a low frequency sound detectable at the belly surface, ranging from 11 to 40 Hz. To study the relationship between the muscular sound and the intensity of the contraction a sound myogram (SMG) was recorded by a contact sensor from the biceps brachii of seven young healthy males performing 4-s isometric contractions from 10% to 100% of the maximal voluntary contraction (MVC), in 10% steps. Simultaneously, the electromyogram (EMG) was recorded as an index of muscle activity. SMG and EMG were integrated by conventional methods (iSMG and iEMG). The relationship between iSMG and iEMG vs MVC% is described by parabolic functions up to 80% and 100% MVC respectively. Beyond 80% MVC the iSMG decreases, being about half of its maximal value at 100% MVC. Our results indicate that the motor unit recruitment and firing rate affect the iSMG and iEMG in the same way up to 80% MVC. From 80% to 100% MVC the high motor units' discharge rate and the muscular stiffness together limit the pressure waves generated by the dimensional changes of the active fibres. The muscular sound seems to reflect the intramuscular visco-elastic characteristics and the motor unit activation pattern of a contracting muscle. 相似文献
137.
138.
Knaus M Cameroni E Pedruzzi I Tatchell K De Virgilio C Peter M 《The EMBO journal》2005,24(17):3000-3011
Regulated interactions between microtubules (MTs) and the cell cortex control MT dynamics and position the mitotic spindle. In eukaryotic cells, the adenomatous polyposis coli/Kar9p and dynein/dynactin pathways are involved in guiding MT plus ends and MT sliding along the cortex, respectively. Here we identify Bud14p as a novel cortical activator of the dynein/dynactin complex in budding yeast. Bud14p accumulates at sites of polarized growth and the mother-bud neck during cytokinesis. The localization to bud and shmoo tips requires an intact actin cytoskeleton and the kelch-domain-containing proteins Kel1p and Kel2p. While cells lacking Bud14p function fail to stabilize the pre-anaphase spindle at the mother-bud neck, overexpression of Bud14p is toxic and leads to elongated astral MTs and increased dynein-dependent sliding along the cell cortex. Bud14p physically interacts with the type-I phosphatase Glc7p, and localizes Glc7p to the bud cortex. Importantly, the formation of Bud14p-Glc7p complexes is necessary to regulate MT dynamics at the cortex. Taken together, our results suggest that Bud14p functions as a regulatory subunit of the Glc7p type-I phosphatase to stabilize MT interactions specifically at sites of polarized growth. 相似文献
139.
Vossen M Edelstein J Majzoub RK Maldonado C Perez-Abadia G Voor MJ Orhun H Tecimer T Francois C Kon M Barker JH 《Plastic and reconstructive surgery》2005,115(2):529-538
Although vascularized bone and joint allotransplantation is a promising new treatment option for reconstructing large bone defects, the need for immunosuppressive agents to prevent rejection in these procedures poses a major problem. This problem stems from the fact that several of these agents can cause harmful side effects, such as alterations in bone quality and healing. Therefore, the purpose of this study was to determine what effect the commonly used immunosuppressant regimen cyclosporine A-based combination therapy has on bone quality and healing. In 10 pigs, vascularized bone allografts with skin and muscle components (osteomyocutaneous free flaps) were transplanted from size-matched donor animals. Recipient animals received oral cyclosporine A/mycophenolate mofetil/prednisone therapy for 90 days. Bone quality was studied before and after transplantation by measuring the bone's acoustic velocity and density and calculating the bone's elastic coefficient. Bone healing was assessed using radiographic analysis. Four animals were lost as a result of graft rejection or immunosuppression-related complications before the 90-day endpoint of the study. Although bone specimens taken from the six animals that completed the 90-day protocol had histological signs of rejection, they all seemed to have normal bone healing. Posttransplant bone density values were significantly decreased (p < 0.05) (1544.7 +/- 47.5 kg/m3) as compared with pretransplant values (1722.7 +/- 44.1 kg/m3). Results of the acoustic velocity and elastic coefficients measurements showed a significant decrease (p < 0.05) in posttransplant values (from 3503.0 +/- 165.1 meters/sec to 2963.0 +/- 54.6 meters/sec and from 21.6 +/- 2.2 GPa to 13.6 +/- 0.5 GPa, respectively), indicating diminished bone quality. The findings indicate that cyclosporine A/mycophenolate mofetil/prednisone combination therapy is ineffective in preventing bone rejection, that it decreases bone quality, and that it is associated with systemic toxicity, suggesting that this immunosuppressive regimen at the doses used in this study is not ideal for vascularized bone allotransplantation procedures. 相似文献