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71.
"Dollo's law" states that, following loss, a complex trait cannot reevolve in an identical manner. Although the law has previously fallen into disrepute, it has only recently been challenged with statistical phylogenetic methods. We employ simulation studies of an irreversible binary character to show that rejections of Dollo's law based on likelihood-ratio tests of transition rate constraints or on reconstructions of ancestral states are frequently incorrect. We identify two major causes of errors: incorrect assignment of root state frequencies, and neglect of the effect of the character state on rates of speciation and extinction. Our findings do not necessarily overturn the conclusions of phylogenetic studies claiming reversals, but we demonstrate devastating flaws in the methods that are the foundation of all such studies. Furthermore, we show that false rejections of Dollo's law can be reduced by the use of appropriate existing models and model selection procedures. More powerful tests of irreversibility require data beyond phylogenies and character states of extant taxa, and we highlight empirical work that incorporates additional information. 相似文献
72.
Spatial variations in xylem sap flux density in evergreen oak trees with radial-porous wood: comparisons with anatomical observations 总被引:1,自引:0,他引:1
Makiko Tateishi Tomo’omi Kumagai Yasuhiro Utsumi Toshihiro Umebayashi Yasuki Shiiba Kazunobu Inoue Kiyohiro Kaji Keiichiro Cho Kyoichi Otsuki 《Trees - Structure and Function》2008,22(1):23-30
To estimate whole-tree water use when employing sap flow measurements, integration of the sap flux density (F
d) over the sapwood area is needed. Accordingly, it is necessary to obtain information on the characteristics of stem water
transportation such as spatial variations in F
d and the active xylem area in the stem cross-section. Although evergreen oak trees with radial-porous wood represent a major
component of secondary forests in western Japan, detailed information on their stem water transportation characteristics remains
unclear. In the present study, we used the heat dissipation method (Granier method) to conduct measurements of azimuthal and
radial variations in the F
d of Quercus glauca Thunb. ex Murray, a representative evergreen broad-leaved tree in western Japan. Further, by analyzing the anatomy of the
xylem structure, we examined why F
d varies spatially in the stem cross-section. By using a dye solution injected into a radial hole bored into the tree trunk,
we confirmed that the entire stem is hydroactive. We also compared the spatial variations in F
d and water conductivity per xylem area (K
s) which were estimated by using the observed vessel diameters and their density over the stem cross-section and Hagen–Poiseuille’s
law. Azimuthal and radial variations in F
d reached about 60 and 50% of the maximum values, respectively, and could be explained by spatial variation in K
s. As a result, we obtained statistical parameters describing the spatial variation in F
d in Q. glauca and determined that whole-tree water use estimated from measurements in one direction had at most ±20% potential errors for
studied trees. 相似文献
73.
74.
75.
Many high-elevation lakes in designated wilderness are stocked with native and nonnative fish by state fish and game agencies
to provide recreational fishing opportunities. In several areas, this practice has become controversial with state wildlife
managers who support historical recreational use of wilderness, federal wilderness managers who assert that stocking compromises
some of the ecological and social values of wilderness, and different public groups that support one or the other position.
Herein we examine this controversy from the perspective of the 1964 Wilderness Act, its judicial interpretation, the policies
of the federal agencies, and formal agreements between federal and state agencies. Although some state stocking programs restore
native fish populations, other programs may compromise some of the ecological and social values of wilderness areas. Further,
although current federal regulations recognize state authority for fish stocking, judicial interpretation gives federal agencies
the authority for direct involvement in decisions regarding fish stocking in wilderness. Where there are differences of opinion
between state and federal managers, this judicial interpretation strongly points to the need for improved cooperation, communication,
and coordination between state wildlife managers and federal wilderness managers to balance recreational fishing opportunities
and other wildlife management activities with wilderness values.
Received 28 March 2000; Accepted 16 August 2000. 相似文献
76.
螺旋藻细胞培养与光能利用的关系 总被引:5,自引:0,他引:5
对钝顶螺旋藻(Spirulina platensis
Geitler)细胞培养体系的光衰减以及连续培养条件下藻细胞生长对光能的利用特性进行了分析,结果表明改进的Lambert-Beer定律I=I0exp(-αxL)可较好地描述细胞浓度及光程对光衰减的综合影响;引入平均光强和细胞平均比消光量概念,借鉴Monod方程形式,较好地描述了它们与比生长速率之间的关系,并求得最大比生长速率μm、光强半饱和参数kI、光能维持系数m和得率系数YG分别为μm=1.75/d,kI=1.453×10 相似文献
77.
黑河流域生态经济带分异协调规律与耦合发展模式 总被引:19,自引:2,他引:17
在西北干旱地区建设黑河流域生态经济带,是从根本上高效配置流域水资源,彻底化解流域上,下游利益冲突,实现利益共享,保护流域生态环境,推进流域可持续发展,全面实施国务院黑河流域分水方案的重要途径,通过对黑河流域生态经济带上-中-下游投入产出效益的比较分析和流域上、中、下游生态-生产、生活系统发展分异及互动协调关系的分析,提出了黑河流域生态经济带上-中-下游多维互动的协调耦合发展模式,进而提出了黑河流域生态经济带建设与发展的主要途径,包括推进黑河流域经济发展一体化和集成管理公司化,大力推行全流域水资源的差异化有偿使用制度,实施流动上、中、下游的水权转让贸易,实行规范的流域财政转移支付制度,建立流域资源与生态环境和经济的整合帐户体系,实行跨行政区域河流边界水量水质达标交接制度,等等。 相似文献
78.
最大信息熵原理与群体遗传平衡 总被引:29,自引:0,他引:29
建立了用最大信息熵原理推导群体遗传平衡定律的统一数学模型,并给出了模型的统一解,此解正是Hardy-Weinberg定律所给出的平衡群体的基因型频率,说明当群体信息熵达到最大时,群体基因型频率不再变化,即达到“平衡”。这证明了最大熵分布就是Hardy-Weinberg平衡分布。Hardy-Weinberg平衡定律与最大信息熵原理的内在一致性说明,杂交和随机交配是一个不可逆过程,使群体基因型信息熵增大,无序性增,是选择和近亲交配使群体的信息熵降低,有序性增加,育种过程实际就是调节群体信息熵的过程。过程信息熵的含义是表示一个概率分布的不确定性,最大熵原理意味着在一定的约束条件,选择具有最大不确定性的分布,从而其分布是最为随机的。最大熵原理在信息,工程,天文,地理,图像处理,模式识别等自然科学和社会科学领域都有广泛的成功应用,本文从群体遗传学角度证明了这一原理具有普遍适用性。熵是描述系统状态的函数,而最大熵原理则表明了系统发展变化的趋势,系统的最终状态必然是熵增加至最大值的状态,对于任何系统都是如此。因此,群体遗传系统的平衡定律可以统一用最大熵原理进行判定和描述;任意群体的基因型信息熵在随机交配世代传递时有不断增加的趋势;在一定约束条件下基因型信息熵达到最大值时,就称之为达到遗传平衡。本文将信息论原理应用于群体遗传学研究,揭示了基因信息熵的生物学意义,并表明可以用信息学和控制论的原理和方法来研究群体遗传学问题。 相似文献
79.
80.
Taylor's law (TL), which states that variance in population density is related to mean density via a power law, and density‐mass allometry, which states that mean density is related to body mass via a power law, are two of the most widely observed patterns in ecology. Combining these two laws predicts that the variance in density is related to body mass via a power law (variance‐mass allometry). Marine size spectra are known to exhibit density‐mass allometry, but variance‐mass allometry has not been investigated. We show that variance and body mass in unexploited size spectrum models are related by a power law, and that this leads to TL with an exponent slightly <2. These simulated relationships are disrupted less by balanced harvesting, in which fishing effort is spread across a wide range of body sizes, than by size‐at‐entry fishing, in which only fish above a certain size may legally be caught. 相似文献