全文获取类型
收费全文 | 150477篇 |
免费 | 5645篇 |
国内免费 | 5067篇 |
出版年
2023年 | 584篇 |
2022年 | 667篇 |
2021年 | 2191篇 |
2020年 | 1756篇 |
2019年 | 2111篇 |
2018年 | 13388篇 |
2017年 | 11822篇 |
2016年 | 9472篇 |
2015年 | 4135篇 |
2014年 | 4448篇 |
2013年 | 4829篇 |
2012年 | 9500篇 |
2011年 | 17325篇 |
2010年 | 14726篇 |
2009年 | 10820篇 |
2008年 | 12951篇 |
2007年 | 14173篇 |
2006年 | 3000篇 |
2005年 | 2979篇 |
2004年 | 3108篇 |
2003年 | 2956篇 |
2002年 | 2401篇 |
2001年 | 1626篇 |
2000年 | 1333篇 |
1999年 | 1133篇 |
1998年 | 670篇 |
1997年 | 645篇 |
1996年 | 584篇 |
1995年 | 524篇 |
1994年 | 502篇 |
1993年 | 423篇 |
1992年 | 568篇 |
1991年 | 498篇 |
1990年 | 399篇 |
1989年 | 317篇 |
1988年 | 291篇 |
1987年 | 257篇 |
1986年 | 170篇 |
1985年 | 191篇 |
1984年 | 131篇 |
1983年 | 138篇 |
1982年 | 83篇 |
1981年 | 65篇 |
1979年 | 81篇 |
1978年 | 80篇 |
1977年 | 59篇 |
1976年 | 57篇 |
1973年 | 56篇 |
1972年 | 287篇 |
1971年 | 303篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
1.
Benjamin B Wheatley Gregory M Odegard Kenton R Kaufman Tammy L Haut Donahue 《Biomechanics and modeling in mechanobiology》2017,16(3):1011-1022
The passive properties of skeletal muscle are often overlooked in muscle studies, yet they play a key role in tissue function in vivo. Studies analyzing and modeling muscle passive properties, while not uncommon, have never investigated the role of fluid content within the tissue. Additionally, intramuscular pressure (IMP) has been shown to correlate with muscle force in vivo and could be used to predict muscle force in the clinic. In this study, a novel model of skeletal muscle was developed and validated to predict both muscle stress and IMP under passive conditions for the New Zealand White Rabbit tibialis anterior. This model is the first to include fluid content within the tissue and uses whole muscle geometry. A nonlinear optimization scheme was highly effective at fitting model stress output to experimental stress data (normalized mean square error or NMSE fit value of 0.993) and validation showed very good agreement to experimental data (NMSE fit values of 0.955 and 0.860 for IMP and stress, respectively). While future work to include muscle activation would broaden the physiological application of this model, the passive implementation could be used to guide surgeries where passive muscle is stretched. 相似文献
2.
3.
4.
5.
Ji Guo Su Xiao Ming Han Xiao Zhang Yan Xue Hou Jian Zhuo Zhu Yi Dong Wu 《Journal of biomolecular structure & dynamics》2016,34(3):560-571
Protein collective motions play a critical role in many biochemical processes. How to predict the functional motions and the related key residue interactions in proteins is important for our understanding in the mechanism of the biochemical processes. Normal mode analysis (NMA) of the elastic network model (ENM) is one of the effective approaches to investigate the structure-encoded motions in proteins. However, the motion modes revealed by the conventional NMA approach do not necessarily correspond to a specific function of protein. In the present work, a new analysis method was proposed to identify the motion modes responsible for a specific function of proteins and then predict the key residue interactions involved in the functional motions by using a perturbation approach. In our method, an internal coordinate that accounts for the specific function was introduced, and the Cartesian coordinate space was transformed into the internal/Cartesian space by using linear approximation, where the introduced internal coordinate serves as one of the axes of the coordinate space. NMA of ENM in this internal/Cartesian space was performed and the function-relevant motion modes were identified according to their contributions to the specific function of proteins. Then the key residue interactions important for the functional motions of the protein were predicted as the interactions whose perturbation largely influences the fluctuation along the internal coordinate. Using our proposed methods, the maltose transporter (MalFGK2) from E. Coli was studied. The functional motions and the key residue interactions that are related to the channel-gating function of this protein were successfully identified. 相似文献
6.
Despite our extensive knowledge of insulin-like growth factor 1 (IGF1) action on the growing skeleton, its role in skeletal homeostasis during aging and age-related development of certain diseases is still unclear. Advanced glycation end products (AGEs) derived from glucose are implicated in osteoporosis and a number of diabetic complications. We hypothesized that because in humans and rodents IGF1 stimulates uptake of glucose (a glycation substrate) from the bloodstream in a dose-dependent manner, the decline of IGF1 could be associated with the accumulation of glycation products and the decreasing resistance of bone to fracture. To test the aforementioned hypotheses, we used human tibial posterior cortex bone samples to perform biochemical (measurement of IGF1, fluorescent AGEs and pentosidine (PEN) contents) and mechanical tests (crack initiation and propagation using compact tension specimens). Our results for the first time show a significant, age-independent association between the levels of IGF1 and AGEs. Furthermore, AGEs (fAGEs, PEN) predict propensity of bone to fracture (initiation and propagation) independently of age in human cortical bone. Based on these results we propose a model of IGF1-based regulation of bone fracture. Because IGF1 level increases postnatally up to the juvenile developmental phase and decreases thereafter with aging, we propose that IGF1 may play a protective role in young skeleton and its age-related decline leads to bone fragility and an increased fracture risk. Our results may also have important implications for current understanding of osteoporosis- and diabetes-related bone fragility as well as in the development of new diagnostic tools to screen for fragile bones. 相似文献
7.
S T Chen L C Lo S H Wu K T Wang 《International journal of peptide and protein research》1990,35(1):52-54
2-Oxazolidone derivatives formed through an intramolecular reaction in the process of alkaline treatment of urethane-type N-protected peptides of which the N-terminal residues were Ser or Thr having unprotected hydroxyl groups. In oder to avoid this side reaction, the esters of these peptides could be cleaved by enzymatic hydrolyses instead of saponification. 相似文献
8.
Ralf Schwamborn 《Reviews in Fish Biology and Fisheries》2018,28(3):587-605
Length-based methods are the cornerstone of many population studies and stock assessments. This study tested two widely used methods: the Powell–Wetherall (P–W) plot and the Lmax approach (i.e., estimating L∞ directly from Lmax). In most simulations, P–W estimates of the ratio total mortality/growth (Z/K ratio) were biased beyond acceptable limits (bias?>?30%). Bias in Z/K showed a complex behavior, without possible corrections. Estimates of asymptotic length (L∞) were less biased than Z/K, but were very sensitive to intra-cohort variability in growth and to changes in the occurrence of large individuals in the sample. Exclusion of the largest size classes during the regression procedure or weighing by abundance does not solve these issues. Perfect linearization of the data and extremely narrow confidence intervals for Z/K will lead users to erroneous overconfidence in outputs. Clearly, the P–W method is not suitable for the assessment of Z/K ratios of natural populations. Estimation of L∞ may be tentatively possible under very specific conditions, with necessary external verifications. Also, this study demonstrates that there is no way to estimate L∞ directly from Lmax, since there is no particular relationship to expect a priori between L∞ and Lmax. Errors in estimating L∞ directly affect the estimate of the growth constant K and all other subsequent calculations in population studies, stock assessments and ecosystem models. New approaches are urgently needed for length-based studies of body growth (e.g., unconstrained curve fit with subsequent bootstrapping), that consider the inherent uncertainty regarding the underlying data and processes. 相似文献
9.
Genetic association mapping has been widely applied to determine genetic markers favorably associated with a trait of interest and provide information for marker-assisted selection. Many association mapping studies commonly focus on main effects due to intolerable computing intensity. This study aims to select several sets of DNA markers with potential epistasis to maximize genetic variations of some key agronomic traits in barley. By doing so, we integrated a MDR (multifactor dimensionality reduction) method with a forward variable selection approach. This integrated approach was used to determine single nucleotide polymorphism pairs with epistasis effects associated with three agronomic traits: heading date, plant height, and grain yield in barley from the barley Coordinated Agricultural Project. Our results showed that four, seven, and five SNP pairs accounted for 51.06, 45.66 and 40.42% for heading date, plant height, and grain yield, respectively with epistasis being considered, while corresponding contributions to these three traits were 45.32, 31.39, 31.31%, respectively without epistasis being included. The results suggested that epistasis model was more effective than non-epistasis model in this study and can be more preferred for other applications. 相似文献
10.