全文获取类型
收费全文 | 2096篇 |
免费 | 184篇 |
国内免费 | 108篇 |
出版年
2023年 | 47篇 |
2022年 | 30篇 |
2021年 | 42篇 |
2020年 | 59篇 |
2019年 | 83篇 |
2018年 | 66篇 |
2017年 | 59篇 |
2016年 | 66篇 |
2015年 | 76篇 |
2014年 | 83篇 |
2013年 | 115篇 |
2012年 | 65篇 |
2011年 | 77篇 |
2010年 | 82篇 |
2009年 | 98篇 |
2008年 | 105篇 |
2007年 | 100篇 |
2006年 | 76篇 |
2005年 | 83篇 |
2004年 | 66篇 |
2003年 | 58篇 |
2002年 | 62篇 |
2001年 | 72篇 |
2000年 | 51篇 |
1999年 | 51篇 |
1998年 | 31篇 |
1997年 | 25篇 |
1996年 | 38篇 |
1995年 | 27篇 |
1994年 | 26篇 |
1993年 | 32篇 |
1992年 | 25篇 |
1991年 | 36篇 |
1990年 | 22篇 |
1989年 | 24篇 |
1988年 | 23篇 |
1987年 | 32篇 |
1986年 | 24篇 |
1985年 | 16篇 |
1984年 | 25篇 |
1983年 | 22篇 |
1982年 | 22篇 |
1981年 | 18篇 |
1980年 | 24篇 |
1979年 | 22篇 |
1978年 | 17篇 |
1976年 | 13篇 |
1975年 | 12篇 |
1974年 | 16篇 |
1973年 | 11篇 |
排序方式: 共有2388条查询结果,搜索用时 12 毫秒
1.
Peng Chen Pranjal Swarup Wojciech Michal Matkowski Adams Wai Kin Kong Su Han Zhihe Zhang Hou Rong 《Ecology and evolution》2020,10(7):3561-3573
- As a highly endangered species, the giant panda (panda) has attracted significant attention in the past decades. Considerable efforts have been put on panda conservation and reproduction, offering the promising outcome of maintaining the population size of pandas. To evaluate the effectiveness of conservation and management strategies, recognizing individual pandas is critical. However, it remains a challenging task because the existing methods, such as traditional tracking method, discrimination method based on footprint identification, and molecular biology method, are invasive, inaccurate, expensive, or challenging to perform. The advances of imaging technologies have led to the wide applications of digital images and videos in panda conservation and management, which makes it possible for individual panda recognition in a noninvasive manner by using image‐based panda face recognition method.
- In recent years, deep learning has achieved great success in the field of computer vision and pattern recognition. For panda face recognition, a fully automatic deep learning algorithm which consists of a sequence of deep neural networks (DNNs) used for panda face detection, segmentation, alignment, and identity prediction is developed in this study. To develop and evaluate the algorithm, the largest panda image dataset containing 6,441 images from 218 different pandas, which is 39.78% of captive pandas in the world, is established.
- The algorithm achieved 96.27% accuracy in panda recognition and 100% accuracy in detection.
- This study shows that panda faces can be used for panda recognition. It enables the use of the cameras installed in their habitat for monitoring their population and behavior. This noninvasive approach is much more cost‐effective than the approaches used in the previous panda surveys.
2.
In Quantitative Microbial Risk Assessment, it is vital to understand how lag times of individual cells are distributed over a bacterial population. Such identified distributions can be used to predict the time by which, in a growth-supporting environment, a few pathogenic cells can multiply to a poisoning concentration level.We model the lag time of a single cell, inoculated into a new environment, by the delay of the growth function characterizing the generated subpopulation. We introduce an easy-to-implement procedure, based on the method of moments, to estimate the parameters of the distribution of single cell lag times. The advantage of the method is especially apparent for cases where the initial number of cells is small and random, and the culture is detectable only in the exponential growth phase. 相似文献
3.
The copy frequency distribution of a transposable element family in a Drosophila melanogaster natural population is generally characterised by the values of the Charlesworths' model parameters α and β (Charlesworth & Charlesworth, 1983). The estimation of these parameters is made using the observed distribution of the occupied sites in a population sample. Several results have been interpreted as due either to the influence of stochastic factors or to deterministic factors (transposition, excision, selection…). The accuracy of this method was tested by estimations performed on samples from simulated populations. The results show that with the sample size usually used for natural population studies, the confidence intervals are too large to reasonably deduce either the element copy number distribution or the values of transposition and excision rate and selective coefficients. 相似文献
4.
Kung-Jong Lui 《Biometrical journal. Biometrische Zeitschrift》1995,37(8):965-971
Three simple interval estimates for the risk ratio in inverse sampling are considered. The first two interval estimates are derived on the basis of Fieller's Theorem and the delta method with the logarithmic transformation, respectively. The third interval estimate is derived on the basis of an F-test statistic proposed by BENNETT (1981) for testing equal probabilities of a disease between two comparison groups when the disease is rare. To evaluate the performance of these three methods, a Monte Carlo simulation is used to compare the actual coverage probability with the nominal confidence level for each method and to estimate the expected length of the corresponding confidence interval in a variety of situations. On the basis of the results found in the simulation, we have concluded that the method with the logarithmic transformation is either equivalent to or better than the other two methods for all situations considered here. 相似文献
5.
Erkki P. Liski 《Biometrical journal. Biometrische Zeitschrift》1989,31(3):313-316
Conditions for superiority of the minimum dispersion estimator over another with respect to the covariance matrix are derived when the vector parameter of a regression model is subject to competing stochastic restrictions. The restrictions may also consist both of a deterministic part and a stochastic part. 相似文献
6.
L. P. Lefkovitch 《Biometrical journal. Biometrische Zeitschrift》1991,33(8):899-912
By using deviance standardized residuals, the seemingly unrelated regression estimation procedure is extended to generalized linear models, and fitted by an iterative procedure. The matrix of cross products of standardized residuals is asymptotically multivariate normal, and can be used for further multivariate analyses and for hypothesis testing. 相似文献
7.
For flexible peptides, nuclear Overhauser Effects (NOE) experiments do not provide enough information to ensure a correct definition of their solution structure. The use of distance constraints, derived from the knowledge of proton chemical shifts, is developed to restrict the number of possible conformations. In the case of flexible molecules, randomization appears as an important factor of the correct estimation of the chemical shifts from the 3D structure. The refinement of the solution structure of the highly flexible AVP-like parallel dimer is described to illustrate this process. 相似文献
8.
W. C. Louv Ph. D. 《Biometrical journal. Biometrische Zeitschrift》1987,29(1):81-92
The simultaneous estimation of individual growth curves and a mean growth curve is accomplished by weighted least squares. A polynomial curve is fitted for each individual and the polynomial parameters are linear functions of parameters corresponding to covariates. A simple, computationally efficient variance-covariance estimator is derived. The resultant estimate is used in the weighted least squares estimation. The results are compared to empirical Bayes estimation. 相似文献
9.
10.
A statistical test is described to verify the characteristics of the biological information contained in the dynamics of the flowering process. The test focuses on interactions between the pollen index and climatic variables to investigate if the biological indicator can synthesise the information of the pre-flowering phases. The multiple-regression model is built upon two pre-flowering climate macro-indicators extracted by Principal Component Analysis (PCA) and the optimised pollen index is obtained by non-parametric estimation. The empirical analysis is applied to 15 stations located in southern Italy in regions that have a longstanding tradition of olive production. Using the variance explained, we find that an optimised pollen index is fairly well predicted by the pre-flowering climatic data. We conclude that the optimised pollen index makes more parsimonious the modelling for predicting olive production. 相似文献