全文获取类型
收费全文 | 35963篇 |
免费 | 2866篇 |
国内免费 | 4764篇 |
出版年
2023年 | 758篇 |
2022年 | 875篇 |
2021年 | 1201篇 |
2020年 | 1220篇 |
2019年 | 1746篇 |
2018年 | 1399篇 |
2017年 | 1238篇 |
2016年 | 1189篇 |
2015年 | 1132篇 |
2014年 | 1816篇 |
2013年 | 2543篇 |
2012年 | 1496篇 |
2011年 | 1660篇 |
2010年 | 1337篇 |
2009年 | 1724篇 |
2008年 | 1705篇 |
2007年 | 1869篇 |
2006年 | 1625篇 |
2005年 | 1480篇 |
2004年 | 1279篇 |
2003年 | 1196篇 |
2002年 | 1094篇 |
2001年 | 831篇 |
2000年 | 766篇 |
1999年 | 673篇 |
1998年 | 643篇 |
1997年 | 541篇 |
1996年 | 472篇 |
1995年 | 495篇 |
1994年 | 476篇 |
1993年 | 446篇 |
1992年 | 404篇 |
1991年 | 434篇 |
1990年 | 321篇 |
1989年 | 309篇 |
1988年 | 323篇 |
1987年 | 264篇 |
1986年 | 302篇 |
1985年 | 479篇 |
1984年 | 580篇 |
1983年 | 317篇 |
1982年 | 454篇 |
1981年 | 442篇 |
1980年 | 392篇 |
1979年 | 296篇 |
1978年 | 221篇 |
1977年 | 236篇 |
1976年 | 211篇 |
1975年 | 160篇 |
1973年 | 180篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
DNA replication is a fundamental process of the cell that ensures accurate duplication of the genetic information and subsequent transfer to daughter cells. Various pertubations, originating from endogenous or exogenous sources, can interfere with proper progression and completion of the replication process, thus threatening genome integrity. Coordinated regulation of replication and the DNA damage response is therefore fundamental to counteract these challenges and ensure accurate synthesis of the genetic material under conditions of replication stress. In this review, we summarize the main sources of replication stress and the DNA damage signaling pathways that are activated in order to preserve genome integrity during DNA replication. We also discuss the association of replication stress and DNA damage in human disease and future perspectives in the field. 相似文献
12.
Accurately estimating patient-specific rupture risk remains a primary challenge in timing interventions for abdominal aortic aneurysms (AAAs). By re-analyzing published biaxial mechanical testing data from surgically repaired human AAAs, material anisotropy emerged as a potentially important determinant of patient-specific lesion progression. That is, based on a new classification scheme, we discovered that anisotropic aneurysmal specimens correlated with increased patient age at surgery when compared with more isotropic specimens (79.7 vs. 70.9 years, p<0.002), despite no significant difference in maximum diameter. Furthermore, using an idealized axisymmetric, finite-element growth and remodeling model of AAA progression, we found that both the initial axial extent of elastin loss and ongoing damage to elastin in the shoulder region of the AAA directly affected the degree of anisotropy as the lesion evolved, with more extensive insults increasing the anisotropy. This effect appeared to be mediated by alterations in axial loading and subsequent differences in orientation of deposited collagen fibers. While the observed increased age before surgical intervention may suggest a potential benefit of anisotropic remodeling, future biaxial tests coupled with pre-surgical data on expansion rates and detailed theoretical analyses of the biostability of a lesion as a function of anisotropy will be required to verify its clinical relevance to patient-specific rupture risk. 相似文献
13.
Activity of salivary glands in secreting honey‐elaborating enzymes in two subspecies of honeybee (Apis mellifera L) 下载免费PDF全文
Aliaa A. Al‐Sherif Adel M. Mazeed Mohamed A. Ewis Emad A. Nafea El‐Seid E. Hagag Ahmed A. Kamel 《Physiological Entomology》2017,42(4):397-403
The activity of invertase, glucose oxidase and amylase in the cephalic (post‐cerebral) and thoracic salivary glands is determined in Egyptian and Carniolan honeybees (Apis mellifera L). For this purpose, three ages of worker bees are selected for enzyme assays. The results show that the three target enzymes are detected in the two glands during the three worker ages, except invertase, which cannot be detected in the cephalic gland of newly emerged bees of both subspecies. In both glands, the secretion of invertase is highest, followed by amylase and then glucose oxidase. In Carniolan bees, invertase secretion of the cephalic and thoracic glands increases gradually with age. In Egyptian bees, invertase increases with age only in the cephalic gland, whereas, in the thoracic gland, the highest secretion activity is detected in 10–15‐day‐old bees. The highest amounts of glucose oxidase and amylase in the cephalic gland are detected in newly emerged individuals of both Egyptian and Carniolan bees. In the thoracic gland, however, the highest activity of both enzymes is recorded only in newly emerged Egyptian bees. The results are discussed in the light of bee management and biological aspects of the two subspecies. 相似文献
14.
15.
16.
Rashi Verma Monika Yadav Rajabrata Bhuyan Shweta Aggarwal Arnab Nayek 《Journal of receptor and signal transduction research》2016,36(6):601-616
Computer-aided antibody engineering has been successful in the design of new biologics for disease diagnosis and therapeutic interventions. Interleukin-6 (IL-6), a well-recognized drug target for various autoimmune and inflammatory diseases such as rheumatoid arthritis, multiple sclerosis, and psoriasis, was investigated in silico to design potential lead antibodies. Here, crystal structure of IL-6 along with monoclonal antibody olokizumab was explored to predict antigen–antibody (Ag???Ab)-interacting residues using DiscoTope, Paratome, and PyMOL. Tyr56, Tyr103 in heavy chain and Gly30, Ile31 in light chain of olokizumab were mutated with residues Ser, Thr, Tyr, Trp, and Phe. A set of 899 mutant macromolecules were designed, and binding affinity of these macromolecules to IL-6 was evaluated through Ag???Ab docking (ZDOCK, ClusPro, and Rosetta server), binding free-energy calculations using Molecular Mechanics/Poisson Boltzman Surface Area (MM/PBSA) method, and interaction energy estimation. In comparison to olokizumab, eight newly designed theoretical antibodies demonstrated better result in all assessments. Therefore, these newly designed macromolecules were proposed as potential lead antibodies to serve as a therapeutics option for IL-6-mediated diseases. 相似文献
17.
Troy MacAvelia Ahmad Ghasempoor 《Computer methods in biomechanics and biomedical engineering》2014,17(12):1285-1294
The advent of haptic simulation systems for orthopaedic surgery procedures has provided surgeons with an excellent tool for training and preoperative planning purposes. This is especially true for procedures involving the drilling of bone, which require a great amount of adroitness and experience due to difficulties arising from vibration and drill bit breakage. One of the potential difficulties with the drilling of bone is the lack of consistent material evacuation from the drill's flutes as the material tends to clog. This clogging leads to significant increases in force and torque experienced by the surgeon. Clogging was observed for feed rates greater than 0.5 mm/s and spindle speeds less than 2500 rpm. The drilling simulation systems that have been created to date do not address the issue of drill flute clogging. This paper presents force and torque prediction models that account for this phenomenon. The two coefficients of friction required by these models were determined via a set of calibration experiments. The accuracy of both models was evaluated by an additional set of validation experiments resulting in average R2 regression correlation values of 0.9546 and 0.9209 for the force and torque prediction models, respectively. The resulting models can be adopted by haptic simulation systems to provide a more realistic tactile output. 相似文献
18.
19.
20.